I started using BackTrack 4 years ago then moved up to BackTrack 5 until it was discontinued by Offensive Security and replaced with Kali Linux. It is a great OS full of penetration tools. No, I am not sponsored by Offensive Security or anyone else but I respect them and the products they put out. Nethunter is another great tool from them I have used and still use.
I will write up some of the tools I used and how I use them. There are a ton of write ups out there and mine will just show some of the mistakes I made and how I fixed them.
If you want to get into penetration testing I would pick an area like Web, Mobile, Network, etc. and start reading about how to pen test that area. And I would download Kali and start playing with that too.
There is no one book or website that will teach you everything you want or need to know about pen testing.