Im 15 going on a cruise for the first time? what should i expect?

Im 15 going on a cruise for the first time.. i have o clue what its gunna be like. whats fun to do??? im going on the carnival triumph for 5 nights.. what should i wear to dinner?? sumone told me i should dress up so i went shopping and got a few dressy dresses.. do i have to dress up to go to lunch and breakfast too????im going with my mom and dad so is it easy to make ffriends?? where should i go to make new friends, and is there arcades?? or movie theatres or anything?? im goin in 12 days, and i would really appreciate some help!:):) thanks sooo much!:):):)