Documenting GNOME and the many GNOME applications is a very big project. We would love to have you in the project. Here are some links to get you started:
Just follow the directions at mail.gnome.org. Feel free to introduce yourself on the list and indicate what type of documentation you are interested in writing. (This list is low volume.)
This document covers everything from installing documentation-related packages to use of DocBook markup and document templates to make getting started fast and simple.
You can find the GDP team at the #docs channel on irc.gnome.org. Point X-Chat or your favorite IRC client there to meet other GDP Team members, find out more about the GDP, or just chat about GNOME documentation.
There are many things to do in the GDP. The most common task is to write user documentation for a particular application (see step below). However, there are many other ways people can contribute to the GDP. We also need content editors, markup editors, indexers, glossary authors, testers, packagers(tgz, RPM, and deb), people to convert and markup non-DocBook docs, developers, help system designers, etc. Whatever your skill, we probably need it. You may also look at our Task lists to see some of our current tasks which we need people to work on. Pick whatever interests you most and email the GDP mailing list indicating what you would like to do.
Most GDP documentation is in writing user documentation for GNOME applications and components. However, we also write developer documentation, too. To find out the status of various documentation items and find a document to work on, check out the GNOME Documentation Status Table (DocTable). This page keeps track of the status of each GDP document. After you decide what you will work on, make sure you are added to the DocTable so others don't duplicate your work. You may also want to email the mailing list to let others know what you are working on.