My 1981 yamaha xj650 doen't crank. The oil light comes on when I push the ignition. I would like to know what that means so I can fix it.

You have a bad kick stand safety switch, look where the kick stand mount is, their is a switch with 3 wires, connect two of them together and try it, if not hook the other two together, that will fix your problem.

Be sure you have a fully charged battery and then start checking all the connections to the startter-does the starter engage but not turn the engine over (low battery or bad connections)or does the starter not engage (could also be bad battery but also could indicate starter problem)