I recently got my bike running, and it's super fun to ride, but the lights don't work. I've scoured the internet trying to understand electrical issues on motorcycles but I am hopelessly unknowledgeable. I don't know much about electrical circuits. I've heard that I should clean the place where the ground connects to the frame. Can someone help me understand what this is and where it is? Also, if you have further advice please share.

Could be as simple as a blown headlight bulb, so remove the lens assembly from the bowl, disconnect the wires/plug attached to it and bench test the bulb by  connecting it directly to a 6v battery. Make a note of which terminal the black (negative) wire attaches to and replicate that direct from the battery, with the positive going to the other two in turn (high and low beam). You won't do any harm by not making these connections, but you won't complete a circuit if you attach the battery wires to the high and low beam terminals.

If the bulb works in either/both tests, then your problem lies elsewhere. If it doesn't, then you have a blown bulb and need a new headlight. I would also suggest fitting a 6v voltage regulator.

Perhaps do this test first and then report back here? Also, I'm assuming that no-one has fitted a 12v conversion kit to your bike?