I have seen two types of guns. One you have to pull off the spark plug lead and the gun connect in series to the spark plug ie it is "patched in" between the spark plug and the lead. And the other type (far easier) clips over the spark plug lead and works on induction. Both types then have two aligator clips which go to the battery to give it power. The spark plug lead provides a trigger for the strobe which you point at the crankshaft pulley (usually). There should be a mark on this and a few marks on the timing cover (behind the pulley). When the light is flashing the pulley should appear to stand still and the mark on it should line up with the correct mark on the timing cover, usually around 10deg. BTDC. If it doesn't you adjust it by either rotating the dizzy or adjusting the vernier adjustment on it (consult manual). If it is controlled by computer then this is all pointless (get it, "pointless", ahh forget it). What engine is it?