A Source Control tool is a central database that holds all your code.
Instead of everyone working on a single copy of the code and emailing and FTPing code around, everyone does their work on a copy of the code they got from that database.
When they complete a new feature, they 'commit' the changes to the central database. These tools are clever enough to work out what changed, if your change conflicts with another coder's changes, and to update the central database's copy of the code.
Then, at any time, you can go to that central database and ask for the latest code (containing other people's changes) or, even more usefully, get any previous version of the code. So the msdn article is saying, "So what if visual studio broke your code, go back to your source database and get the last version that isn't broken and start over again with that."
As you can see, having that kind of power would be useful even for a single coder. You can see how your project is coming along, check out what changed and when, and be able to go back to a previous version if you stuff something up and can't remember or work out what it was.
It also means all your code is in a central place, which is excellent for making backups. I have everything I've ever done that I cared about under source control and backed up daily.
Subversion is a source control database made by
Collabnet. It is free and excellent. That is the server.
TortoiseSVN is a Windows add-in that you use as a client to Subversion. You tell it the URL of the Subversion server and it is able to do all the source control operations from within Windows menus. Again, it is free and pretty excellent.
With that installed, you can just go Right Click, Add and put your files in source control. It's that simple.
You can have the server and the client on one machine. The server is (or was, anyway, looks like they've made some fairly radical changes recently) just a Windows service that runs in the background when the PC starts up.
There are other source control databases, Git is becoming popular and is free and is an interesting variation on distributed source control, Perforce is good but probably not free, CVS (free) and Microsoft SourceSafe (not free) are not so good.
Jim