There is a sticker on the vehicle (the one that tells the year and engine size under the hood) that has the timing information on it. It will tell you what you should set the timing to and also which wire you need to disconnect to 'retard' the engine. When you have done this the number markings are on the harmonic balancer, the very bottom pulley of the motor. Hook the clips up to the battery and the clip with the hole in it around the cylinder number one wire. Then aim the gun at the numbers and it will tell you where it is timed. To change the timing you need to loosen the bolt holding the distributor and rotate it until the timing is correct.