Encoding descriptions - where?

Hi! I tried to search for good descriptions about everything in DivX encoding, but I've found only small scripts; for special programs, or small details. Where can I find a great, circumstantial description, which interprets all the concepts (aspect ratio, bitrate, etc.), is clear, and easy to understand? If not here, or anywhere on the internet, then for example a book title? I'm not new in DivX encoding, but I don't understand what I do. I want to know things, which doesn't claim an informatic knowledge.

Contradiction? 

OK. I mean, that I've already made a lot of DivX films in good quality, but I don't know, what I did in details. I know, that a film with more than 850-900 bitrate is acceptable, but I don't know, what is bitrate correctly. I know, that aspect ratio can be 16:9 or 4:3, and I can see it in DGIndex preview, but I don't know, what is aspect ratio accurately. I have ideas about all of these notions, and I know a little bit about them, but I would like to understand it narrowly. Shall I be an informatitian?

Please review the documents at the links you've been provided. In particular, the DivX User Guide should answer most, if not all of your questions. It was very well written, includes graphical examples, and is available in multiple languages.

Thank You for your help! I think, the DivX Guide is the best description, and if I don't understand things with it, I'll do this "not-understanding" in the future with others. By the way, bitrates, and ratios were only examples of my imperfect knowledge, but now I'm closer with 2% to my aim. : )