Netstat is a the command that lists all current network connections, connection statistics, and routing tables on your computer
The default netstat command will give you listing of all the ports open on your computer
Netstat will tell you which programs are sending/receiving information to and from your computer
References:
Boyle, R., & Proudfoot, J. (n.d.). DOS Commands. In Applied information security labs: A hands-on approach (Second ed., p. 13).