Buttons easy to use. You need to go to edit->project settings-> input manager and to make settings for horizontal. Then you need to go in your player controller and ad something like
moveInput = Input.GetAxis("Horizontal");
rb.velocity = new Vector2(normalSpeed * moveInput, rb.velocity.y);
where rb is rigidbody2d but you need to freeze Z rotation in rb. But you can try to watch some tutorials on youtube