How to set TDC
 

I've seen a lot of threads saying to 'set #1 to TDC' but none on how to do that. Does anyone have any advice or a link that would help explain?

I just replaced the lower intake manifold gasket on a 1998 4.3L and when putting everything back together, I believe I came up a tooth off on the distributor. The engine fires and runs pretty well, but the check engine soon light is on, and the AutoZone readout says this is most likely the cause.

Also (and I don't plan on driving it much), to what extent could I damage the engine under these conditions?

Thanks in advance for any help.