To view and browse pages on the Web, all you need is a web browser. To publish pages on the Web, you need a web server.
A web server is the program that runs on a computer and is responsible for replying to web browser requests for files. You need a web server to publish documents on the Web. One point of confusion is that the computer on which a server program runs is also referred to as a server. So, when someone uses the term web server, she could be referring to a program used to distribute web pages or the computer on which that program runs.
When you use a browser to request a page on a website, that browser makes a web connection to a server using the HTTP protocol. The server accepts the connection, sends the contents of the requested files, and then closes the connection. The browser then formats the information it got from the server.
On the server side, many different browsers can connect to the same server to get the same information. The web server is responsible for handling all these requests.
Web servers do more than just serve files. They're also responsible for managing form input and for linking forms and browsers with programs such as databases running on the server.
As with browsers, many different servers are available for many different platforms, each with many different features and ranging in cost from free to very expensive. For now, all you need to know is what the server is there for; you'll learn more about web servers in Lesson 18, "Putting Your Site Online."