If you are a newcomer, you might be afraid by its sheer size. Don’t worry, but in any case, do not give up: as stated in the very beginning of this document,
That is to say everything exposed in this document is considered to be known. If it is written but you didn’t know, you are wrong. If it is not written and was not clearly reported in the news, we are wrong.
Basically this document contains three kinds of information:
What you must read and know since the very beginning of the project. This includes most the following chapters: Introduction (except the History section), Instructions, and Evaluation.
You should read these parts as and when needed. This includes mostly Compiler Stages.
This information is provided to help you: just go there when you feel the need, Tools, and Source Code. If you want to have a better understanding of the project, if you are about to criticize something, be sure to read History beforehand.
There is additional material on the Internet: