Often when I read the manual, I think that we should take a collection up to have Lars psycho-analysed.
-- Bill Pringlemeir
There's only one Gnus Manual, but it's available in a number of formats:
In addition, an illustrated version is also available:
The length of these documents varies from about 500 pages to about 550 pages, depending on which version of the manual you choose.
A FAQ (list of Frequently Answered Questions) is also available, and is very useful.
You can also read the info pages inside Emacs by saying C-h i m gnus RET