The Geronimo project uses the Subversion version control system. If you're new to Subversion, you can check out the online book about Subversion. Note that we are currently using Subversion 1.1.x (there are separate versions of the book covering 1.0 and 1.1).
If you just want to browse the source code, you can use the ViewCVS web interface to Subversion. This is current at all times.
Anyone can check code out of Subversion. You only need to specify a username and password in order to update the Subversion repository, and only Geronimo committers have the permissions to do that. We run Subversion over standard HTTPS, so hopefully you won't have problems with intervening firewalls.
Again, anyone can do this. Use a command like:
svn checkout https://svn.apache.org/repos/asf/geronimo/trunk geronimo
Any Geronimo committer should have a shell account on svn.apache.org. Before you can commit, you'll need to set a Subversion password for yourself. To do that, log in to svn.apache.org and run the command svnpasswd.
Once your password is set, you can use a command like this to commit:
svn commit
If Subversion can't figure out your username, you can tell it explicitly:
svn --username you commit
Subversion will prompt you for a password, and once you enter it once, it will remember it for you. Note this is the password you configured with svnpasswd, not your shell or other password.
Refer to the Wiki page for the build procedure. It typically takes 10-30 minutes for a full build, and it needs to be run while online in order to download or update a large number of dependencies.