The first is SET, the second is CLOCK and the thirth is RESET (up to down). The CLOCK input is necessary to make the circuit work, if is not in 1 just you can not make a change in it. Normaly the circuit has one output in 1 and the other in 0. To change the output secuence it needs to set the CLOCK input in 1, and now you can send an impulse at SET input and change the OUTPUT secuence. To return to the normal secuence, needs the CLOCK input in 1 too, and send an impulse at the RESET input.
