Hi there, it's difficult to give advice without more information, however, I'm assuming that your train (from Paris?) makes the connection at Lyon Part-Dieu station.
I also assume that you're getting the last 21:05 connection from Lyon to Le Puy? Although possible, it's probably cutting it a bit fine, but in the worst case scenario you'll just have to get a hotel or hostel and then pay €25 for a regional connection to Le Puy the next morning. (The French trains are generally quite punctual, give or take 10 mins... and of course barring strike action, or occasionally having to wait for other trains to clear the tracks, etc)
Lyon Part-Dieu is't too difficult to navigate, although each track is accessed via its own set of stairs/escalator, so you first have to go downstairs after disembarking your train, and then make your way up again to catch the next one. Depending on the time of day, there can be a 'bottle-neck' effect as everyone tries to go up/ down a single escalator, which might significantly slow you down (and bearing in mind that your trip also coincides with the French Easter holidays...)
However, as far as I remember there are only 11 tracks in Lyon. Once you've arrived, there should be screens everywhere, showing train times and departure tracks (just make sure your screen says 'departs' and not 'arrivees'!) Here's what will shown on the screens (in real time!), so save this link and you might even be able to check on the train before disembarking if you have wifi:
http://www.gares-en-mouvement.com/fr/frlpd/horaires-temps-reel/dep/
You can probably figure it out, but it goes: type of train (mainline TGV or regional TER? this info should be on your ticket), train number, time, destination, delays ('retard'), and most importantly, the track number. You might also be able to ask the conductor for help when he comes to punch your ticket. The French train staff are usually lovely and often happy to practice a bit of English, as long as you first *try* asking in French, however bad you might sound!