If you have a chip in the key, wait 3-4 minutes, after attempting the first start, then try again. Sometimes the VATS socket gets alittle worn. If it starts, this suggests the key socket is worn.
Turn lights on, are they bright? Try to start, lights dim and no crank? Or starter engaged and no turn over? Poor connection(s).
Attempt to start, and wiggle gearshift in and around neutral, could be worn neutral safety switch or maladjusted switch.
Attempt to start for 5-8 seconds, then turn off. Feel battery connections, The one that is hot, is a bad connection. Disasssemble it, clean it, and reassemble. Hopefully you didn't use those clamp-on battery cable connections. They are a quick fix, but, over time can introduce more problems later.
Others here may have some good suggestions,
Oh, by the way, Welcome to the club.