A modem is the thing that hooks your computer to the phone line or cable system. Unless your computer is at an office or school that is already wired for a direct Internet connection, you need a modem. Modems come in all sorts of shapes and sizes. Some are separate boxes, known as external modems, with power cords and with cables that plug in to the computer and the phone line. Others are inside the computer, with just a cable for the phone, and some are tiny credit-card-sized things you slide into the side of your laptop computer. (They still have a cable for the phone — some things never change.)

Matching the variety of physical sizes is an equally wide variety of internal features. The speed at which a modem operates (or the rate at which it can stuff computer data into a phone line) ranges from a low of 2,400 bits per second (bps, commonly but erroneously called baud) to 56,000 bps (usually abbreviated 56K, and the bps part is dropped). Some modems can act as fax machines, and some can't. Some have even more exotic features, such as built-in answering machines.

Most computers sold in the past couple of years come with built-in modems. If you already have a modem, use it. If you have to buy a modem, get a 56K, since anything slower (like 28.8 or 14.4) won't be much cheaper. For external modems, be sure to get a cable to connect the modem to your computer, and be sure that it has connectors that match the computer — three different types of plugs may be on the back of a computer. Almost any modem made in the past ten years is adequate for an initial foray on the Internet. However, if you use a slow (old) modem, don't expect to do what your friends with a fast (new) modem can do — you'll be quickly frustrated.

Note to laptop computer owners: If your computer has credit-card–sized PC Card slots but no built-in modem, get a PC Card modem that fits in a slot so that you don't have to carry around a separate modem when you take your computer on the road. Although it costs more, it's worth it.