What are "sets" and "reps"?
Every exercise has, among other parameters, "sets" and "reps".
A rep is a repetition. This means that you should repeat an exercise x times (x being the number that is set in PhysiApp).
A set is a set of repetitions. This means that you should repeat the above sets x times.
See the sample exercise below. This exercise is to be completed 10 times. And then 9 times.