Suppose you are working on some brand new machine. You've just installed Eclipse and you want to get your source from the repository. It's easy. Just go to the SVN perspective and add the repository. Find your source and right click and choose checkout. Now you have the source on your local machine.
Next, you will want to save your changes. This you do by committing, though I think I already mentioned it. Another common thing you will want to do is get any new changes from the server. Suppose both you and a friend are working on the same project and you have been waiting for him to complete a particular class so that you can use it. Once he's finished and committed his changes, you can add them to your working copy of the source by going to the java perspective, right clicking on the project going to team and clicking UpdateToVersion.