You can use SteamCMD to download the dedicated server.
Mainly the same as launching any other source server, specify the org+ident for game and map and it'll all download automatically.
Players connect through your servers Steam ID, there's no need to worry about port forwarding or anything.
Your server will pop up in the select gamemode of choice:
Make sure you have updated the server to the latest version. If you have Steam installed on the host machine, make sure it is updated.