Versions includes its own copies of Subversion 1.4 through 1.8 and does not require that Subversion be separately installed, though Xcode 5 includes Subversion 1.7.9 by default.
If you want to use a different command line version of Subversion or want to install a newer version than what is included with Xcode, you can find installers for various SVN releases here.
For more information about what it means to use a certain release of Subversion, see this page.