Facebook Canvas URL and Secure Canvas URL

Hi, I am using Buddypress default theme and I installed the Ultimate Facebook.

All I want is to be able to register to my website with facebook. But I am having big trouble seeting two things the Canvas URL and the Secure Canvas URL.

I searched everywhere, I have spent more than 6 hours on this.. As I am a complete newbie I dont know how to code this canvas URL and where do I have to upload it. And I cant find a step by step guide, like, Create these files, insert this codes in and drop them in directory B.

The login button appears in my website, but when I put my email and password i get "Page not Found".

Thank you very much!