First - take your time making decisions. In particular bet-sizing. It should be obvious, but you won't have the benefit of poker software telling you exactly what is in the pot. Plus, there are many more distractions in a live game. So slow down. If in doubt about pot-size or protocol, ask the dealer.
Second, don't be intimidated. A $50 buy-in is not going to attract your area's top professionals. The quality of play will be similar to a low buy-in online tournament.
Third - you asked what to say and how to conduct yourself. Be friendly, polite, and professional, but say as little as possible. However, when it is your turn to act, clearly articulate your intentions to the dealer. "Call". "Raise". "Check". Most of the time it's obvious what you are doing, but it's noisy and distracting in there. Make the dealer's job as easy as possible and avoid unfortunate mistakes Also pay attention to what others say or do. You might just pick up a tell or two. Your brain will remember things, even if you don't.
Fourth - You'll be nervous at the beginning, so play very tight early. I presume you won't be playing with your last $50 - and the idea is to have fun. So ease into it the first few hand. After a few
hands, you'll have relaxed and settled in. Then just enjoy yourself, win or lose.
Fifth - when you win a hand, don't provide color commentary about your thought process to the rest of the table. You will sound like an idiot.