I think it is important to ask if you are talking specifically about the Source Control Management plugin for DDE 8.5.2 on OpenNTF or if your talking specifically about Subversion ( SVN ).
The SCM plugin on OpenNTF is just a translation layer that converts NSFs to flat file structures on disk and then keeps them in sync so when you modify form or XPage etc it updates the flat file version on the disk.
The SCM plugin, on it's own, does not do the actual source control checkins, commits, pulls. For this you need a second plugin. In the documentation that comes with the SCM Plugin it describes how you can install the Subversive Plugin which is just a SVN plugin, however there are other source control systems out there, my personal preference is Mercurial and the MercurialEclipse plugin on JavaForge works perfectly in DDE, you could also look at GIT, Bazzar, Dacks or CVS as other possible source control modules.
These secondary plugins are the ones that do the actual source control for you. After converting the project into a flat file structure using IBM's plugin you then go to the navigator pane in the DDE ( you may need to open that pane as it's not a default ) and then you see two projects, one for the NSF and one for the flat file version. On the flat file version you can then see the 'Team --> Share' menu which allows you to link it to your source control server of your choice and all the Source Control menu options will only exist on that flat file version of the project.
I hope this helps. If you need further info then check out my blog ( http://www.qtzar.com ) where I've been writing about Source Control in Domino lately.
Declan Lynch.