here are some options
Mazuli, if you are behind a firewall you have to find out what your external IP address is so that people can connect to you, you also have to make sure that you choose Internet as the server option when your creating it, default its Lan, and will only show up on your Local area network.
I had an issue where my firewall won't let anyone go threw it so i had to disconnect it, I am running my server from work now on a dedicated T1, cause its the only option i have seeing as I need all 3 of my PCs at home to connect.
Counterstike seemed easy, thats just cause it did everything behind the scenes, and it uses ports that are already open on your router most likely. Doing a tad more research might find your answer.