Once you launch the Terminal, you can use the many facilities that Mac OS X provides at the command line, an environment that's quite a bit more powerful than the graphical interface you may be used to viewing. As a user, you have an account that gives you:
A place in the filesystem where you can store your files
A username that identifies you and lets you control access to files
An environment you can customize
In this chapter, you'll see how all the thousands of files on your Mac are organized, how to learn more details about any given file, and how to move around through Mac OS X's filesystem. You'll see that the Finder has been hiding quite a lot of information from you, entire directories with thousands of files that are invisible from the Finder but easily found and explored within the Terminal.
A file is the unit of storage in Mac OS X. A file can hold anything: text (a report you're writing, a to-do list), a program, digitally encoded pictures or sound, and so on. All of those are just sequences of raw data until they're interpreted by the right program.
Files are organized into directories (more commonly referred to as folders on the Aqua side of the Mac). A directory is actually a special kind of file where the system stores information about other files. You can think of a directory as a place, so that files are said to be contained in directories, and you work inside a directory. It's important that you realize that ...