The first time I field stripped my new Garand I had difficulty getting the trigger guard back to lock back into place. Try as I might I just couldn't make it flex enough by pushing as indicated in the instructions. I found out later this is common in Garands with new stocks as the mechanism hasn't completely seated into the wood yet so it binds. Until it does seat you're actually supposed to hit it with a mallet!
Well I come from a generation where you just didn't treat your weapon like that. If you have to force something into place that means you're doing it wrong and you should stop immediately before you screw it up, but this really how you're supposed to do it.
Get the manuals. Like any military rifle there is a wealth of documentation on it and the M1 especially.
Just beware of "M1 Thumb"! It is real and it is painful but luckily easy enough to avoid once you know how it happens.