You ll need to have enough memory to run the software. If your computer is connected to a network, you may not need any more hardware. Many networks are permanently connected to the Internet. In addition to the connection, an online service, like America OnLine, provides content like discussion forums, information articles, and other web pages and services. Usually you use a telephone line and a modem to connect your computer to the ISP's server computer, which is connected to the Internet.
Costs vary widely.
Different accounts at the same ISP provide different services and different amounts of time online. There is no standard pricing. Your ISP will tell you how to configure your computer to connect. It's not really that hard to do. Modems come in several different speeds.