Movenments

There are many ways to create player movement in Unity 3D, such as rigidbody and character controller. In this movenment, you can move like normal player, you can jump, you can crouch and this has gravity which is not by default in character controller.

Code

// VARIABLES
[SerializeField] private float walkSpeed;
[SerializeField] private float runSpeed;
private float moveSpeed;

[SerializeField] private float gravity;
[SerializeField] private float groundCheckSize;
[SerializeField] private LayerMask groundLayer;
[SerializeField] private Transform groundCheck;
private bool isGrounded;
private Vector3 velocity;

[SerializeField] private float jump;

private CharacterController controller;

// REFFFERNCE
//////////////////////
// RUN ONCE AT START
private void Start()
{
    // Getting Character controller from the children.
    controller = GetComponentInChildren<CharacterController>();
}

// UPDATE EVERY FRAME
private void Update()
{
    // MOVENMENT FUNCTION
    Move();
}

private void Move()
{
    // Checking if player is grounded.
    isGrounded = Physics.CheckSphere(groundCheck.position, groundCheckSize, groundLayer);

    // If player is grounded then stop applying gravity.
    if (isGrounded && velocity.y < 0)
    {
        // Setting velocity to -2 for being on safe side.
        velocity.y = -2;
    }

    // VARIABLE
    float moveX = Input.GetAxis("Horizontal");
    float moveZ = Input.GetAxis("Vertical");
    
    // Getting where to move the player.
    Vector3 move = new Vector3(moveX, 0, moveZ);
    // Making it so it move on player's X and Z axis insted of global axis.
    move = transform.TransformDirection(move);
    
    // Condition for walking and running speed
    if (move != Vector3.zero && !Input.GetKey(KeyCode.LeftShift))
    {
        // Move with walk speed.
        Walk();
    }
    else if (move != Vector3.zero && Input.GetKey(KeyCode.LeftShift))
    {
        // Move with walk speed.
        Run();
    }
    
    // Checking if player is on ground.
    if (isGrounded)
    {
        // Make Player jump.
        Jump();
    }
    
    // If Left alt is pressed down make player crouch.
    if (Input.GetKeyDown(KeyCode.LeftAlt))
    {
        // Making Player crouch.
        transform.localScale = new Vector3(1, 0.5f, 1);
    }
    // When left alt is released make player normal.
    if (Input.GetKeyUp(KeyCode.LeftAlt))
    {
        // Making Player normal.
        transform.localScale = new Vector3(1, 1, 1);
    }
    
    // Adding either move speed or run speed.
    move *= moveSpeed;
    // Moving Player
    controller.Move(move * Time.deltaTime);
    
    // Increasing velocity with respect of gravity.
    velocity.y += gravity * Time.deltaTime;
    // Applying gravity on player.
    controller.Move(velocity * Time.deltaTime);
}

// WALK FUNCTION
private void Walk()
{
    // Setting move speed to walk speed.
    moveSpeed = walkSpeed;
}

// RUN FUNCTION
private void Run()
{
    // Setting move speed to run speed.
    moveSpeed = runSpeed;
}

// JUMP FUNCTION
private void Jump()
{
    // If player use jump button.
    if (Input.GetButtonDown("Jump"))
    {
        // Changing velocity to make player jump
        velocity.y = Mathf.Sqrt(jump * -2 * gravity);
    }
}

Note: Make an empty gameObject(ground check) and put it on player feet or in other tearms put it below player object. Then drag and drop that object inside player then again drag that ground check object in inspector and insert it in the place of Ground Check. Now click on your ground and them select layer as Ground. Now set groundCheckSize to 0.2. Now set ground layer to ground in player. You are ready to go.

Thank You