In a traditional page layout document, everything comes in one special file. Graphics and any other multimedia are frequently embedded directly in that file itself, requiring a special file type that other programs may not be able to deal with.
Web pages are different.
They use a very ordinary file type, and graphics, sounds, movies, etc. are simply referred to. They must reside in separate files. While this makes it easy to deal with the files themselves in many different programs, and it allows the viewer to download only what multimedia he or she desires, it does make it neccessary to learn a little about what these files are made of and how they relate. This means that you can use nearly any text editor you want to create a web page. There's more to a web page than just text.