A file server is a big box that holds all the computer programs. Many computers hook-up to the file server and share the same programs. A computer doesn't have very many programs alone. A computer cannot share its programs with another computer. A file server has many programs and many computers are hooked into the file server.
Many computers can share the same programs at the same time if they are hooked up to a file server.
The Internet is a file server of file servers. The file servers are connected world-wide like a web. First you need a computer and a phone so people can reach you. Then you need a modem so the computer can talk on the phone. They will give you a phone number that your computer can use to get on the Internet.