A set is when you do an exercise for a set number of reps. A rep is doing the complete movement of the exercise once. If I did 2 sets of curls for 8 reps, that would mean I did curls 8 times, rested and did curls again 8 more times. Rest anywhere from 2-4 minutes in between sets, 5 minutes on really heavy movements like deadlifts; no more then 5 minutes max.