From MEPIS Documentation Wiki
Netstat is an important tool for keeping your system secure. It can tell you a great deal about what is going on with your networking.
To see what your system is currently connected to:
To also see what ports are listening on your machine:
To see which processes are managing which connections:
You will probably see a good number of listening ports, and probably a few established connections, particularly if you are using some kind of network application like a browser or newsreader. Listening ports represent services on your computer that are open to network connection, such as a web server, ssh server, or ftp server. Most port numbers are assigned to certain services, these are known as "well known ports". Disabling services you don't use will close some of these ports, and help keep your system more secure.