Check out example codes for "c sharp download player controller". It will help you in understanding the concepts better.

Code Example 1

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

public class PhysicsObject : MonoBehaviour {

    public float minGroundNormalY = .65f;
    public float gravityModifier = 1f;

    protected Vector2 targetVelocity;
    protected bool grounded;
    protected Vector2 groundNormal;
    protected Rigidbody2D rb2d;
    protected Vector2 velocity;
    protected ContactFilter2D contactFilter;
    protected RaycastHit2D[] hitBuffer = new RaycastHit2D[16];
    protected List<RaycastHit2D> hitBufferList = new List<RaycastHit2D> (16);


    protected const float minMoveDistance = 0.001f;
    protected const float shellRadius = 0.01f;

    void OnEnable()
    {
        rb2d = GetComponent<Rigidbody2D> ();
    }

    void Start () 
    {
        contactFilter.useTriggers = false;
        contactFilter.SetLayerMask (Physics2D.GetLayerCollisionMask (gameObject.layer));
        contactFilter.useLayerMask = true;
    }

    void Update () 
    {
        targetVelocity = Vector2.zero;
        ComputeVelocity ();    
    }

    protected virtual void ComputeVelocity()
    {

    }

    void FixedUpdate()
    {
        velocity += gravityModifier * Physics2D.gravity * Time.deltaTime;
        velocity.x = targetVelocity.x;

        grounded = false;

        Vector2 deltaPosition = velocity * Time.deltaTime;

        Vector2 moveAlongGround = new Vector2 (groundNormal.y, -groundNormal.x);

        Vector2 move = moveAlongGround * deltaPosition.x;

        Movement (move, false);

        move = Vector2.up * deltaPosition.y;

        Movement (move, true);
    }

    void Movement(Vector2 move, bool yMovement)
    {
        float distance = move.magnitude;

        if (distance > minMoveDistance) 
        {
            int count = rb2d.Cast (move, contactFilter, hitBuffer, distance + shellRadius);
            hitBufferList.Clear ();
            for (int i = 0; i < count; i++) {
                hitBufferList.Add (hitBuffer [i]);
            }

            for (int i = 0; i < hitBufferList.Count; i++) 
            {
                Vector2 currentNormal = hitBufferList [i].normal;
                if (currentNormal.y > minGroundNormalY) 
                {
                    grounded = true;
                    if (yMovement) 
                    {
                        groundNormal = currentNormal;
                        currentNormal.x = 0;
                    }
                }

                float projection = Vector2.Dot (velocity, currentNormal);
                if (projection < 0) 
                {
                    velocity = velocity - projection * currentNormal;
                }

                float modifiedDistance = hitBufferList [i].distance - shellRadius;
                distance = modifiedDistance < distance ? modifiedDistance : distance;
            }


        }

        rb2d.position = rb2d.position + move.normalized * distance;
    }

}

Code Example 2

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

[RequireComponent(typeof(Rigidbody2D))]
[RequireComponent(typeof(CapsuleCollider2D))]

public class CharacterController2D : MonoBehaviour
{
    // Move player in 2D space
    public float maxSpeed = 3.4f;
    public float jumpHeight = 6.5f;
    public float gravityScale = 1.5f;
    public Camera mainCamera;

    bool facingRight = true;
    float moveDirection = 0;
    bool isGrounded = false;
    Vector3 cameraPos;
    Rigidbody2D r2d;
    Collider2D mainCollider;
    // Check every collider except Player and Ignore Raycast
    LayerMask layerMask = ~(1 << 2 | 1 << 8);
    Transform t;

    // Use this for initialization
    void Start()
    {
        t = transform;
        r2d = GetComponent<Rigidbody2D>();
        mainCollider = GetComponent<Collider2D>();
        r2d.freezeRotation = true;
        r2d.collisionDetectionMode = CollisionDetectionMode2D.Continuous;
        r2d.gravityScale = gravityScale;
        facingRight = t.localScale.x > 0;
        gameObject.layer = 8;

        if(mainCamera)
            cameraPos = mainCamera.transform.position;
    }

    // Update is called once per frame
    void Update()
    {
        // Movement controls
        if ((Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.D)) && (isGrounded || r2d.velocity.x > 0.01f))
        {
            moveDirection = Input.GetKey(KeyCode.A) ? -1 : 1;
        }
        else
        {
            if (isGrounded || r2d.velocity.magnitude < 0.01f)
            {
                moveDirection = 0;
            }   
        }

        // Change facing direction
        if (moveDirection != 0)
        {
            if (moveDirection > 0 && !facingRight)
            {
                facingRight = true;
                t.localScale = new Vector3(Mathf.Abs(t.localScale.x), t.localScale.y, transform.localScale.z);
            }
            if (moveDirection < 0 && facingRight)
            {
                facingRight = false;
                t.localScale = new Vector3(-Mathf.Abs(t.localScale.x), t.localScale.y, t.localScale.z);
            }
        }

        // Jumping
        if (Input.GetKeyDown(KeyCode.W) && isGrounded)
        {
            r2d.velocity = new Vector2(r2d.velocity.x, jumpHeight);
        }

        // Camera follow
        if(mainCamera)
            mainCamera.transform.position = new Vector3(t.position.x, cameraPos.y, cameraPos.z);
    }

    void FixedUpdate()
    {
        Bounds colliderBounds = mainCollider.bounds;
        Vector3 groundCheckPos = colliderBounds.min + new Vector3(colliderBounds.size.x * 0.5f, 0.1f, 0);
        // Check if player is grounded
        isGrounded = Physics2D.OverlapCircle(groundCheckPos, 0.23f, layerMask);

        // Apply movement velocity
        r2d.velocity = new Vector2((moveDirection) * maxSpeed, r2d.velocity.y);

        // Simple debug
        Debug.DrawLine(groundCheckPos, groundCheckPos - new Vector3(0, 0.23f, 0), isGrounded ? Color.green : Color.red);
    }
}

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