If you're trying to set up a server on your personal computer and you don't know if there's an open port to use, you should give a try to Port Detective.
As you may guess by reading its name, Port Detective is a Windows software tool designed to scan you system and inform you if there's any open and available port that can be then used for setting up a server.
It's not quite an app addressed to beginners, but Port Detective does an excellent job for those who wish to check certain ports. The main window makes this easy, especially because it shows the most common ports that can be used for servers, be they FTP, HTTP, POP3, SMTP or VNC.
So just pick the ports you wish to verify and hit the “Check” button to start the process. You need an Internet connection to use the application and, in case a firewall is installed on your system, you must grant access to the Internet.
Once the scan comes to an end, Port Detective launches a web browser instance and shows information on every single port, along with status and suggestions on how to solve certain issues.
Port Detective is a quick and reliable tool and works just fine on all Windows versions, but you need administrator privileges to use it on Windows 7.
Overall, Port Detective does what it says and although it's not at all aimed at beginners, it still makes everything very easy for those who know what to do after launching the app.