8-20 reps. WTH? Well, the thing is, YOU might get the most out of this workout by doing reps of 20. But someone else might get more out of doing heavier sets of 8. And the thing about THAT is the person who gets the most out of heavy sets of 8 today, will get more out of medium sets of 20 next time. You have to go with what your body tells you.
Don't know what your body wants just yet? Cool do sets of 12.
You’re looking for max pump today. What's pump? It's that point during a set where your muscles burn/ache but can keep going. So you do. You want to stop because it hurts (not real pain here, just pump) but you have a few more reps in you. You get those last 3-5 reps and walk away with your muscles feeling bigger and fuller - AKA "pumped."
Supersets = Two sets of exercises performed back to back followed by little or no rest.