Grab yourself a copy of ubuntu run it as root its more fun just don't get compromised, I never ran ubuntu not as root regardless all the complaints and people saying I was silly pft. Do what ever you want test your system learn commands. There are forums dedicated to these operating systems that have beginners guides etc.
Learning commands can be a long and painstakingly process. Well worth it in the end.
Backtrack runs alot of pentesting tools so you can really find yourself in the deep end really fast if your not to careful. The best thing for you to do since your new to the whole process is grab a virtual machine install ubuntu on it and test it out if you break it just reset your virtual machine. Easy.