Help with my Dash move?

Hi, guys. I'm trynig to code a player controller with a Dash function that allows my character to dash from a point to another, by using the "Dash" button that i set at the Input Manager (left shift). I've watched 5 ou 6 YouTube tutorials and none have worked for me.

I did tried some answers here in the Unity Answer section, but i've concluded that something is wrong with my code.

Could someone please help me?

 public class PlayerController : MonoBehaviour {
 
 
     public float speed;
     public float jumpForce;
     public float secondJumpForce;
     private float moveInput;
 
     private Rigidbody2D rb;
 
     private bool facingRight = true;
 
     private bool isGrounded;
     public Transform groundCheck;
     public float checkRadius;
     public LayerMask whatIsGround;
 
     private int extraJump;
     public int extraJumpValue;
     
     //Dash tentative
     public float startDashTime;
     float dashTime;
     public float dashSpeed;
     public Input dash;
 
     // Use this for initialization
     void Start () {
         rb = GetComponent<Rigidbody2D>();
         extraJump = extraJumpValue;
         dashTime = startDashTime;
     }
 
 
     private void FixedUpdate()
     {
 
         isGrounded = Physics2D.OverlapCircle(groundCheck.position, checkRadius, whatIsGround);
 
         moveInput = Input.GetAxis("Horizontal");
         rb.velocity = new Vector2(moveInput * speed, rb.velocity.y);
         
 
         if (facingRight == false && moveInput > 0)
         {
             Flip();
         }
         else if(facingRight == true && moveInput < 0)
         {
             Flip();
         }
 
 
         
 
     }
 
     // Update is called once per frame
     void Update ()
     {
         if (isGrounded == true)
         {
             extraJump = extraJumpValue;
         }
         Jumping();
         Dash();
         /*
          * "Blink" system, used while dash does not work
          * if (Input.GetKeyDown(KeyCode.Z))
         {
             transform.position += new Vector3(dashSpeed * Time.deltaTime, 0.1f,0f);
         }
         */
     }
 
     private void Jumping()
     {
         if (Input.GetButtonDown("Jump") && extraJump > 0)
         {
             rb.velocity = Vector2.up * secondJumpForce;
             extraJump--;
         }
         if (Input.GetButtonDown("Jump") && extraJump == 0 && isGrounded == true)
         {
             rb.velocity = Vector2.up * jumpForce;
         }
     }
 
     void Flip()
     {
         facingRight = !facingRight;
         Vector3 Scaler = transform.localScale;
         Scaler.x *= -1;
         transform.localScale = Scaler;
     }
 
     void Dash()
     {
         if (Input.GetButton("Dash"))
         {
             rb.velocity = Vector2.right * dashSpeed;
             
         }
     }
 }