What are ports Back in the 1970s, when the United States were developing a communication system called the Internet, they realized that they wanted this communication protocol to be widely flexible. To accommodate different protocols, they invented ports. Port can be imagined as doors. Doors that close and open according to what protocol you use. For example, whenever you want to access hlds101.tk, your computer open the port 80 and let's the information pass through. Then, at the hlds101.tk server room, a router decides on where to lead the port 80. That decision is done by port forwarding. Port forwarding is assigning to which computer to deliver a communication through a specific port. Why do we need to forward ports on routers?
Routers are used to connect multiple computers using the same internet connection, without port forwarding, the router wouldn't know to which computer give the packets. If I disable my firewall on my router, I don't need to forward ports, right?
Wrong! Firewalls just block ports as there are a lot of security flaws in Windows. And, you should never disable a firewall or use a unfirewalled computer! I'm reaaaaaaaaaly desperate and I don't want to forward ports, can I bypass it?
You can do something called "Virtual DMZ".... That will open all the ports on the computer you choose, but be warned, install a software firewall on your server before you do that! I don't have a router... What do I do?
You gently move your mouse to the navigation menu on the left and choose the next category! Modems don't require port forwarding because they connect directly to your computer/server. Note for Windows XP and Windows Server 2003 users:
If you are behind a firewalled router, please DISABLE the integrated Windows firewall. If it's the only firewall that protects you, please get a more powerful firewall (hint: ZoneAlarm)! | 
