Of course the reason to have directories and subdirectories is so they can contain files. You will usually see a list of the files in a directory. You might just see the names of the files, or you might see the names with little icons that represent what kind of information the files contain. Often if you double-click on a file, something will happen. If the file is a program, it will run. If it is a document, the operating system will try to open the proper program for viewing or editing the file. For example, if I have a program called "Letter.doc" on my drive somewhere, I might navigate my way to that file and double - click on it. When I do so, my operating system recognizes by the ".DOC" extension that this is a program for Word, and it runs word with my letter loaded up and ready to edit. Cool!