P90X Help: How to gain weight?

Hey im Ryan im 16 years old and i weigh 135 lbs and im really skinny. I just got the P90X DVDs and im really stoked and cant wait to do it i just have some questions about it. 1. Im trying to gain weight in this program so what do i have to change in P90X to do that. 2. That nutrition guide they sent me should i use it? If you guys can answer my questions i would really appreciate it THANKS