i an trying to add touch controls to my game but I cant add a ground check ,I am trying to add a jump button to my game but i cant do a ground check

the code :

public void Jump ()
{

    rb.velocity = new Vector2(rb.velocity.x, jumpForce);
}
,here is the code :

public void Jump ()
{

    rb.velocity = new Vector2(rb.velocity.x, jumpForce);
}