Flying from Dublin Airport to USA?

Well lads. I'm flying from Dublin Airport to the US at the end of the month for the first time (ESTA approved, flying with American Airlines) just visiting. I've never really flown anywhere before and I was wondering if there are any things I should know beforehand travel-wise? My bus is booked to get there 2 hours and 40 minutes before takeoff but I have time to reschedule it if needed. I would really appreciate to hear some people's experiences with this, some tips and advice, general knowledge - anything really. I feel absolutely clueless 🤣 explain it to me like I'm an extraterrestrial. Thanks a bunch I. advance!!