How could you close,open-unused ports?

There is a lot of...noise,amongst not in particularly,high-power users,but also simple home or office users about open ports,net,web ports,being used,either from Windows itself or applications.DCOM is an example of a Windows service,that is "listening" to the net,but also sends data through out it.Skype does that all the time.What about those open ports,can they be "closed'?Should they be...