Subversion (SVN) is the revision control system used in the NEXT software project.
The best source of information on Subversion is its online documentation:
To obtain write permission for the NEXT SVN repository, please get in touch with the repository administrator (at the the time of writing, Justo Martin-Albo).
Useful commands
If you're using a command-line client,
svn help
will list all the available commands. Command-specific help is available, too, e.g.:
svn help checkout
will give you information and usage for the checkout command.