The development guide describes resources that are intended for developers in particular. Many Bochs resources are also covered in the User Guide, including compile instructions, bochsrc options, how to find the mailing lists, etc.
If you are an official SourceForge developer, then you can use SVN with write access. The SVN contains the most recent copy of the source code, and with write access you can upload any changes you make to the SVN server for others to use. The SVN checkout command is identical to the one for normal users, but you might want to get the whole tree to work with branches and tags.
svn co https://svn.code.sf.net/p/bochs/code bochs-svn
Depending on your network connection this may take a long time, since it downloads all files from all branches and tags that exist in the repository at the current revision.