@Ravenmann the first otb tournament I played was pretty relaxed, all boards and clocks should be provided by the tournament organizers. I attended my first tournament in Fredonia NY the organizer and I are friends we had people come from buffalo and I thought for sure I would be crushed. The time control was 25 minutes because we were using the science building at the college we had limited time. Your time control will likely be longer. To my own surprise I made 3rd place and would have made 2nd but I blundered my first game terribly. There was a man there in his 60s that was beating everyone, he was winning the last game against another good player but he lost track of time and flagged though his opponent was down to a king and knight so it was a draw, we were out of time so they didn't play a rematch. It was very fun and rewarding.
Some things to keep in mind:
1. If there is any kind of disagreement with your opponent during the game make sure to call over the organizers or whoever is moderating the tournament to solve the issue. (This happened to me when my opponent was down to a king and I had a king/rook as soon as I took his last piece he declared stalemate to try and save himself I raised my hand and called for the judge immediately even then he played on and I made sure not to stalemate as I walked his king to mate.)
2. Sometimes people will crowd around you to watch your game especially if it's an exciting one. If you can help it, don't let this bother you. I watch one guy probably 20 years old curl up into a ball of anxiety when people went around his table to watch his game. He scooted his chair in leaning over the board while holding his hands up to his face like visors, he was so depressed about people watching that he lost the game rather quickly. Turn all your focus to the board forget your surroundings.
3. Most otb tournaments take all day to complete make sure you at least bring something to drink or figure out what they provide in that area then go from there.
4. Have fun enjoy yourself its normal to be a little anxious but you can still make it a good experience. Some players might try to be intimidating by their stature or making fast moves/ facial expressions ect... ignore all that silliness and use your time wisely. Remember good manners it is customary to shake hands at the beginning/end of each game or when offering a draw.
I really hope this helps a little. Good luck! Make sure to record your games then if you feel like it import them to lichess to share and analyze with the community. Be sure to tag me if you do.