The 56K GameCube Modem Adapter is purely designed for online gaming--it doesn't support regular Internet access or Web browsing. The adapter is easily installed, simply snapping into serial port 1 on the underside of the console and plugging into a standard phone line (an extra jack may be required).
You must use your existing Internet Service Provider (ISP) for online access. Please be aware that some service providers, e.g., AOL, do not allow outside software to access their services without the use of a special login tool. Please contact your service provider if you're not sure whether or not they allow this.