Some very new modems may have a theoretical maximum of 56 Kbps. Very old modems may be as slow as 2400 Kbps. In order to be happy with an Internet connection, you will need at least a 14.4 Kbps modem. In order to use this kind of modem, you must first install the software that came with it. Most modems have between two and four plugs in the back.
External modems have a power plug, and it connects to the power supply.
Internal modems get their power from the computer's power supply. This connects the modem to the computer. If you purchased a new external modem, chances are you also need to buy a serial cable for this plug. Internal modems connect to the computer through the system bus. If you get these backward, it won't hurt the modem, but the modem won't work, either.