The Tao of the IETF is a must read document. If you read nothing else, read this. It's a very thorough introduction to the IETF.
These provide overviews of the tools and processes used by the IETF, technical areas of interest to IETF participants, and updates on the work underway in the IETF Areas.
This explains a number of the acronyms and terms that you may see and hear.
This includes links to their charters. In each charter, there are links to all drafts currently discussed by the WG and to all RFCs that the WG has produced. Also, there are instructions on how to join each WG mailing list.
This is very helpful if you want to find a particular chair to ask questions or discuss an issue.
This statement makes it clear that the rules apply to you personally, as an IETF participant.
This provides introductions to a number of aspects of the Internet Engineering Task Force (IETF) history, structure and operations.