The explosive sets are there to get your primed and also to figure out a band tension (if you are using them) for the AMAP set. If you cannot do two pull ups fast then you might need more assistance for those sets as well as the AMAP set.
I agree on the form video because seeing it will help, but the idea is we want you to move fast. From straight arms to chin at the bar with no middle ground. It is only two reps so put as much effort into moving quickly as you can.