Telephone line, modem, computer, and an ISP are the four things needed to connect to the Internet.
Once you have your computer, you really don't need much additional hardware to connect to the Internet. The primary piece of hardware you need is a modem. ... Dial-up access uses a telephone modem, DSL service uses a DSL modem, cable access uses a cable modem, and satellite service uses a satellite adapter.
Suppose you want to connect your computer to an Internet Service Provider (ISP) using an ordinary phone line. The computer at your end needs a modem to modulate its digital signals (add them on top of an analog telephone signal) so they can travel down the phone line just like the sound of your voice.
When computers connect to each other on the same network, it is called a local area network, or LAN. When multiple networks are connected to each other, it is called a wide area network, or WAN. With this type of network, your home has a network router that connects to your ISP.