VisualSVN automatically adds to Subversion all files you add to your project if the project is under Subversion control. In some cases (such as autogenerated files) you might want to avoid adding some files to the Subversion repository.
There is svn:ignore property which can be set on solution, projects or any other folder in the working copy. You can choose the VisualSVN | Properties context menu command for an item in Solution Explorer and configure which files should be ignored inside the folder. Files satisfying patterns listed in svn:ignore property will not be added to Subversion. For example, you can enter something like svn:ignore = "bin obj *.user *.build-res" .
For further details please refer to the Subversion documentation.