it is your best interest.. if you are not sure what an SVN is.. to not try using that CC quite yet. It usually means the development is more of an Alpha stage (most of the time) and that the developers need more then just "It don't work, why not?".
If you feel gutsy enough.. in a nut shell here is how you use a SVN based CC....
1) download a SVN Client (easy search google, bing, yahoo) for your OS (Windows 32bit/64bit)
2) install said client
3) reboot machine (not always necessary but good practice since it ties into windows components)
4) goto your HB Custom Classes folder and create the folder by which the CC is suppose to be (i.e.: for fpsware's Priest you would create a directory called Fpsware Priest)
5) goto the OP of the CC thread (or the second or third) and you will find a URL that points to the SVN, copy that into your clipboard
6) goto the folder you created within your Custom Classes folder and right mouse click. You will see an option simlitar to "SVN Checkout", click that.
7) Paste the URL you got from step #5 into the sectoin it says to (should be pretty clear where depending on your SVN client) and click OK (or whatever the save/close button is on your SVN client).
8) Right mouse click again on that same folder and now you should see something along the lines of "SVN Update" .. click that
9) Wait for it to finish the sync...
You should be good to go. Please note.. you should have HB closed out (not just stopped) before updating the CC. If you attempt to do the above without closing HB first and then restarting it AFTER you update, will cause issues.
And finally, If you are unable to follow the above steps easily, I would recommend you do not attempt SVN CC"s for now, wait for the developers to put the zip file of it up.
Hope this helps....