Parallel ports are usually 25 pin female connectors. If you're going to connect to a computer that's not in the same room, you'll need to use a modem. This is a unit that plugs into a computer on one side and into the phone line on the other side. As explained in chapter three, the signals that computers use won't travel very far down wires and therefore have to be converted into audio signals, which do travel well through long wires. This is what a modem does.
Modulation is the process of converting digital signals into sound signals.
As well as converting the data into a form in which it can be sent down a phone line, modern modems are able to dial phone numbers and answer incoming calls automatically. They both do exactly the same thing. Both types of modem have their advantages. Internal ones are considerably cheaper and don't require a separate serial card, however they can't necessarily be used with other types of computer. Either way, they are easy to install and operate.