Microsoft Visual SourceSafe (VSS) is now a legacy version control system. It is still supported by Help+Manual but it has been discontinued by Microsoft, so it is no longer possible to obtain a new copy. If you already have it and use it, it still works fine. However, on balance we would generally recommend using the much more modern and powerful Subversion (SVN).
Subversion is advanced open-source software that is very well supported and maintained and it is constantly being refined and improved. It has much better performance than VSS and gives you much greater flexibility. Best of all, it is free, and the client software like Tortoise SVN that you need to interface with the SVN server on your local computer is also of very high quality and free.