Port Test allows you to see if a TCP port on your computer is accessible over the Internet. Many programs and services require you to have open ports to use them properly, for example BitTorrent clients and FTP servers.
For Port Test to determine if your TCP port is open there must be an active listener, i.e. the program/service you are opening ports for must be running. If a port is inacccessible it is usually either a firewall setting or an ISP restriction.
Once it is established that the port you are trying to access is closed there are multiple courses of action to open them. If your PC is behind a router and the router's firewall is disabling access to that particular port you will need to create an exception in the router's firewall settings. How to do this depends heavily of the model of router you own, however usually this requires you to access the router's configuration page in your web browser. Usually this is accessed by going to and address simliar to http://192.168.0.1/, http://10.0.0.1/, etc.
Another reason for blocked ports can be the personal firewall settings on your PC. If you are using a third-party firewall application instructions to unblock ports should be available on the software manufacturers website or in the help window of the application.