You can think of the file structure in an operating system much like that of a "tree". At the bottom of the tree are the roots, and for our purposes, the root directory. Branches can then be followed to the next level which are the directories. From the directories further branches can be followed to the subdirectories, and so on until you reach the files. This structure is valid whether you are working in a command line interface, or a GUI. Also, in much the same way you would have to back down a tree to the root to climb to a different branch, to reach a file that is in a different directory, you must go back to the root directory and then go down the other branches to the file you want. This is true no matter where you are working, but it is more easily to accomplish in a GUI environment. If you are working in DOS or UNIX, getting to a file in a different directory can involve major amounts of typing!