go to File -> GameObject -> cube to create your first GameObject
a handy definition for GameObject: A game object is the base class for all entities in unity

go to Assets -> create -> Material   or  In the Assets window leftClick -> create -> Material

rename it to "green"

click on the RandomWalker GameObject in the Scene view or the Hierarchy

on the left, you will see now the Inspector window showing the GameObjects' properties!

in the MeshRenderer component under Materials you will find the current material(s) assigned.

assign the material you've just created.

Create a Folder in the Assets Window and call it "Materials"
Drag the newly created Material 'green' into the newly created folder "Materials"

In the Inspector (right pane on default) scroll down and click 'Add Component'
Type the name of your new Script in this case "RandomWalker' and press the enter key.
In the Assets Window you'll see the newly created Script.

Create a Folder in the Assets Window and call it "Scripts"
Drag the Script "RandomWalker" into the newly created Folder called Scripts

When the script is created, it normally opens immediately in the IDE that is associated with Unity
in our case, that is Visual Studio Code. You can the associated editor under File -> Preferences -> External Tools

If the editor does not open, you can click with your mouse on the script in the Assets window, generally you can find all Scripts in the folder "Scripts."

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RandomWalker : MonoBehaviour
{
    public float speed = 2f; // speed of movement
    public float range = 3f; // range of movement
    private Vector3 targetPosition;

    void Start()
    {
        targetPosition = transform.position + Random.insideUnitSphere * range;
    }
    
    void Update()
 {
 		// move towards target position
        transform.position = Vector3.MoveTowards(transform.position, targetPosition, speed * Time.deltaTime);
        // if target position is reached, set a new random target position
        if (Vector3.Distance(transform.position, targetPosition) < 0.1f)
        {
            targetPosition = transform.position + Random.insideUnitSphere * range;
        }  
    }
}

A Prefab is a pre-made blueprint for a game object that can be used repeatedly to create instances of that object with the same properties and behaviors. We could for example create a prefab of our random walker with the green material and the RandomWalker script attached.

Please first create a Folder called "Prefabs" if you don't have such a folder in Assets.

We create a prefab, by dragging a GameObject from the Hierarchy to the Assets window, ideally into the folder called "Prefabs"

Create an Empty GameObject with Ctrl+Shift+N   or   GameObject (top bar) -> Create Empty

Name it "SpawnLocation"

Set its Transform component to 0,0,15 in the Inspector (the position of the Camera at 0 , 0 , 0)

In the Inspector click "Add Component", type SimpleSpawn and press the enter key to create a new Script with the name "SimpleSpawn"

Copy the following code into the script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SimpleSpawn : MonoBehaviour
{
    // Start is called before the first frame update
    public GameObject prefab;
    public float spawnInterval = 1.0f;

    void Start()
    {
        InvokeRepeating("spawnObject", spawnInterval, spawnInterval);        
    }

    void spawnObject()
    {
    Instantiate(prefab, transform.position, transform.rotation);
    }
}

In the Inspector under the "Simple Spawn" Script component assign under Prefab our RandomWalker Prefab.

Open the Random Walker Script and after the Class Declaration add:

public float lifetime = 5f; //the lifetime of the GameObject
private float age = 0f; //the age of the GameObject

In the Update ( ) function add: 

age += Time.deltaTime;
         if (age >= lifetime)
        {
            Destroy(gameObject);
        }

Now, every lifetime seconds, the spawned game objects get destroyed.

When our 'random walkers' expire into the ether, it might be more appropriate to just let them fade out instead of seeing them instantly disappear, whenever age >= lifetime is fulfilled and dictates them to be destroyed.

first, we need an additional variable after the class declaration: 

public float fadeTime = 3f;

Then we'll add a coroutine with IEnumerator, add the following block after the last closing bracket } of the Update() function:

IEnumerator FadeOutAndDestroy() {
        Renderer renderer = GetComponent<Renderer>(); // get the renderer component
        Color currentColor = renderer.material.color; // get the current color of the material
        currentColor.a = 1f; // set the alpha to 1 (opaque)
        while (currentColor.a > 0) {  // loop until the alpha is 0 (invisible) 
            currentColor.a -= Time.deltaTime / fadeTime; // fade out the alpha over time
            renderer.material.color = currentColor; // set the new color of the material
            yield return null; // wait for the next frame
        }
        Destroy(gameObject); // destroy the game object
    }

Now we have to make a modification to the Update() function. Instead of Destroy(gameObject) when the condition of the if statement (age >= lifetime) is met, we have to start the coroutine that will fade out the instance and then destroy it! Replace the if statement as follows:

if (age >= lifetime && destroyable)
        {
            StartCoroutine(FadeOutAndDestroy());
        }

this will only work if Material is set to Fade in the inspector:

enabling the Auto Mirror Add-On

Creating subdivisions

Setting up the Material

1. Create a new 3D Unity project 2021.3.15f 
2. If you want to follow along, download the base scene unitypackage 
3. Import the unity package
4. open base scene

1. create a new script in the Folder 'Scripts'
2. Call it "RandomSnake"
3. copy the following code into in

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RandomSnake : MonoBehaviour
{
    public GameObject headPrefab;
    public GameObject segmentPrefab;
    public int segmentCount;
    public float speed;
    public float damper;
    public float spring;
    public float changeDirectionTime = 1.0f;

    private List<GameObject> segments = new List<GameObject>();
    private GameObject head;
    private Vector3 randomDirection;
    private float timeSinceLastDirectionChange;

    void Start()
    {
        // Create head and add it to the segments list
        head = Instantiate(headPrefab, transform);
        segments.Add(head);

        // Create the segments and connect them with hinge joints
        for (int i = 0; i < segmentCount; i++)
        {
            GameObject segment = Instantiate(segmentPrefab, transform);
            HingeJoint hingeJoint = segment.AddComponent<HingeJoint>();
            hingeJoint.connectedBody = segments[i].GetComponent<Rigidbody>();
            hingeJoint.autoConfigureConnectedAnchor = false;
            hingeJoint.anchor = new Vector3(0, 0.5f, 0);
            hingeJoint.connectedAnchor = new Vector3(0, -0.5f, 0);
            hingeJoint.axis = new Vector3(1, 0, 0);

            JointSpring jointSpring = hingeJoint.spring;
            jointSpring.damper = damper;
            jointSpring.spring = spring;
            hingeJoint.spring = jointSpring;

            hingeJoint.useSpring = true;
            segments.Add(segment);
        }

        // Initialize random direction and timer
        randomDirection = Random.insideUnitSphere.normalized;
        timeSinceLastDirectionChange = 0;
    }

    void Update()
    {
        // Move the head in a random direction
        head.GetComponent<Rigidbody>().velocity = randomDirection * speed;

        // Update timer and change direction if needed
        timeSinceLastDirectionChange += Time.deltaTime;
        if (timeSinceLastDirectionChange >= changeDirectionTime)
        {
            randomDirection = Random.insideUnitSphere.normalized;
            timeSinceLastDirectionChange = 0;
        }
    }
}

1. Create a prefab for the head
2. Create a prefab for the body segments 
3. add a rigidbody to both the head and the body prefabs 

"use gravity" and "use kinematic" must be disabled for the rigidbody componens!

1. Add an empty GameObject to the scene at 0,0,0 (Camera should be at 0,0,-10)
2. Rename it "Creature"
3. Add the "RandomSnake" Script to the Creature GameObject in your scene
4. In the Inspector assign the "head" and "segment" prefabs respectively
5.  insert a segment count and values for speed, damper, and direction change time
6. Try out which values work best
7. When good values are determined, drag the Creature GameObject into Assets/Prefabs to make it a prefab

1. Create a new empty GameObject and rename it to SpawnLocation
2. Assign the SimpleSpawn script 
3. Adjust the SimpleSpawn script to add lifetime and fade the material at it's end
4. here is some info on how you can add lifetime to the creatures

Download

Download the latest release from this Github page

unzip

unzip it to C:\Users\YOUR USERNAME\  (Windows)

For Linux and Mac save unzip it to 'home' directory

now you will have a folder there called: ml-agents-release_20

1. Install Anaconda but don't add it to PATH
2. Install Python and add to PATH during the installation.

Anaconda itself is a Python distribution, but it is not recommended to add it to path. We install Python after our Anaconda installation so that python commands can be executed systemwide, but conda commands only when using conda shell, to prevent any interference with other applications using Python.

create conda environment

conda create -n ml-agents python=3.8

activate conda environment

conda activate ml-agents

install pytorch

install Unity ML Agents:

cd ml-agents-release_20/ml-agents-release_20

pip3 install -e ./ml-agents-envs

pip3 install -e ./ml-agents

Downgrade protobuf and install onnx module

pip install protobuf==3.20

pip install onnx

Create a new unity 3D project with an editor version later than 2020 here I use 2021.03.15f1

Under "Location" choose the ml-agents-release-20 folder that you have in your home directory. 

in the newly created Unityproject Install the ML Agents Unitypackage:

Go to window -> package manager -> + -> install from disk

navigate to C:/Users/ml-agents-release-20/ml-agents-release-20/com.unit.ml-agents and click on the package.json

Copy the ml agents assets to your unity project

in your file system navigate to

C:\Users\YOUR_USERNAME\ml-agents-release_20\ml-agents-release_20\Project\Assets

find the folder ML-Agents 📁 and drag it into your newly created and open unity project into the 'Assets' window.

activate the conda environment

conda activate ml-agents

start the training with conda shell

cd ml-agents-release_20/ml-agents-release_20

mlagents-learn config/ppo/Walker.yaml --run-id=walker-001

humanoid character *.fbx 

script for copying rotation and location:

using UnityEngine;

public class FollowObject : MonoBehaviour
{
    public GameObject objectToFollow;
    public Vector3 offset;
    public bool copyPosition = true;
    public bool copyRotation = true;

    private void Update()
    {
        if (copyPosition)
        {
            transform.position = objectToFollow.transform.position + offset;
        }

        if (copyRotation)
        {
            transform.rotation = objectToFollow.transform.rotation;
        }
    }
}