If you'd like to help with documenting Castle, there are two approaches.

1. Build the documentation and patch it: http://castleproject.org/community/getinvolved.html
2. Populate the using.castleproject.org wiki (this site!)

Option #1 is preferred, however if you are unable to build the Castle documentation, or would simply like to quickly help out, #2 is also available. Firstly, take a look at all of the pages tagged with documentation-push. These are existing pages which have been, or are in the process of being, developed for transfer to the Castle Documentation. documentation-in-progress indicates that a page is still in flux. documentation-request-patch indicates that a page needs to be transferred over to the Castle Docs.

If you can't find a documentation-push page matching the documentation you'd like to contribute to, please create a new one and tag it accordingly. Someone will try and get to it as soon as possible after you tag it documentation-request-patch.