www.srcds.com
Best way to get that server setup.
After that, just assign the machine a static IP, and make sure in the command line field, you denote it with a -ip xxx.xxx.xxx.xxx and -port 27015, which is the standard port configuration.
And THEN, after all that is done, go ahead and setup a Gaming Rule for "Steam", and you'll be all set.
If you don't know the ports, check portforward.com/cports
I honestly wouldn't bother with a named dns server, but rather just an IP address instead. Much less hassle, especially if you are running it off of your home connection.