I cant make my character jump

Assuming you are in 2D with a Rigidbody2D:

This code will make you jump by using the "W" key.

 Rigidbody2D rb2d;
 public float jumpHeight; //adjust me in the editor
 
  void Start()
  {
        rb2d = gameObject.GetComponent<Rigidbody2D>();
       jumpHeight = 20f; //how high you want to jump
  }
 
 void FixedUpdate()
 {
         if (Input.GetKeyDown("w"))
         {
             rb2d.AddForce(Vector2.up * jumpHeight);
         }
 }