You might want to check out other programs other than that. Jump Manual is a decent program, but I've seen a few kids at my gym who are in their early teens who tried following Jump Manual and it really didn't help them and they were trying exercises they really had no business trying.
At 13 all you have to do is learn how to squat, learn how to do a deadlift, learn a lunge, and learn to do Box jumps, and jumprope, all of which you can youtube. Do yourself a favor don't complicate things, keep it really simple and you'll see some results.
Sorry for such the delayed response, this forum doesn't seem to get used all that much anymore, JumpUSA tends to do a great job at promoting other programs, but they don't promote themselves. I understand what you're saying and Jump Manual is a quick way to get injured, especially at your age, go to www.vertfreak101.com and go to the forums there, and check out www.Jumpoutthegym.com and check out the user names on youtube "Vertfreak101" and Vertical Jump King (look up channels) the guys who have those 2 programs are 2 friends of mine and they're better than Jump Manual, and you'll learn a lot more from them, if you're on Facebook, check out Vertfreak it has a huge page for it, and Jump Out the Gym. And for websites that will be more helpful than this check out vertfreak101.com or evolutionaryathletics.com or jumpoutthegym.com