//This is a layer that you set up for ground, layers are next to tags on the inspector and you will often need to add one
//The advantage to this is that you can change the layer of several objects to ground and not have to worry about tags or string checks
//To see if your player is on the ground
public LayerMask groundLayer;
//This is the trigger2d collider you add under your players feet so you can easily debug where the box that is supposed to be doing
//ground checks are. While you can declare the size of a box in the physics check I find it easier for new people to be able to see
//the scale
  public BoxCollider2D thisGroundCol;
//A simple float we trip back and forth so that the behavior can know if our player is touching the ground, any ground.
  public float isGrounded;

public void Update()
{
	isGrounded = Physics2D.IsTouchingLayers(thisGroundCol, groundLayer)
	if (Input.GetKeyDown("up") && isGrounded)
             {
				rigidbody2d.velocity = Vector2.up * jumpheight;
             }
        }
}