When you’re ready to raft, you’ll be suited up with a lifejacket. Be sure to select one that fits. A loose jacket will not be much help if you fall overboard. A tight one will just get tighter and more uncomfortable as the day goes on. If you need help with adjustments, ask.
You’ll also be expected to help launch the crafts and to paddle as you go. If you want a cruise where you sit back and do nothing, then book a yacht. Whitewater rafting is a participation sport.
Chat with the other rafters and the guide(s). You’ll learn a lot, and the trip will be more fun if you interact.