How to use Subversion from a Mac:

Download Subversion binaries from http://homepage.mac.com/martinott/

Open a command line terminal (terminal from the spotlight search at top right of your Mac)

To download the whole repository, ype

svn co <URL of your repository, typically starts with https://>

svn up to update (download the latest changes)

svn commit to check in your changes

That's it.