A "set" is a collection of reps (reps=repetitions). If your goal is to complete 20 pushups, you might break your workout up into two sets of 10 reps. This can help you effectively pace yourself.
Discussion
I don’t understand
so you get paid by doing 20 pushups? 
I used the number 20 to explain what a set was since you said you didn’t understand.
We have a game with a bunch of friends where we do 100 push-ups every day until the bitcoin price his $100K USD
No one is getting paid to do push-ups 😂