We provide a central, backed-up, version control service which supports several version control software packages. There is documentation at:
although we do not currently provide end-user tutorials on using version control software.
In general, what we recommend people do is get a project created on Redmine, either by asking one of the existing project admins
to create one, or by requesting to be a project admin themselves, and then filling out a web form to get a repository for your project; then you would use whichever supported version control tool you prefer to check in revisions of your software.
If you need to learn how to use a version control package, you probably want to start with something like one of the O'Reilly books on Subversion or Git:
or you can search on Google, or look on youtube, for online tutorials.