The difference is, with web pages you can write your own gunk. HTML - Hyper Text Markup Language is the language you use to write your own web gunk. Since we're writing our own gunk, we can't use a word processor. Word processors add gunk of their own and the only gunk we want in this file is the gunk we put there ourselves. So we need to use a type of program called a text editor.
Text editors put absolutely no gunk into the files they create.
The only thing that ends up in the file is what you put there yourself. That's what we want. Or you can use SimpleText, which already comes with every Mac. In Windows, you can use NotePad. In these examples, we'll use SimpleText, but the idea is exactly the same.