noob!
You can download the dedicated server
here.
Source Dedicated Server (srcds) has a great guide on setting up a server. You can also have people join your server when you Create Server from the menu, but you'll need to forward ports and give them your real IP (ie, not 192.168.0.1), and add sv_lan 0 to you server cfg. You'll also need a lot of bandwidth to host any halfway decent server.