A:
You put a bobber stop on your line then a plastic bead, then your slip bobber, then your split shot sinker then your hook.
You slide the bobber stop to the place you want the bobber to be above your hook & bait, this sets how deep in the water the bait will be.
When you cast, the shot, hook & bait sink, the bobber moves up the line pushing the bead up until the bead reaches the bobber stop & can't go any further, the bobber can't pass over the bead so the bead & bobber stay where the bobber stop is and the bobber keeps the bait at the depth you set with the bobber stop.