With a typical Unix system, a staff person has to set up a Unix account for you before you can use it. With Mac OS X, however, the operating system installation automatically creates a default user account. The account is identified by your username , which is usually a single word or an abbreviation. Think of this account as your office ”it's your personal place in the Unix environment.
When you log into your Mac OS X system, you're automatically logged into your Unix account as well. In fact, your Desktop and other customized features of your Mac OS X environment have corresponding features in the Unix environment. Your files and programs can be accessed either through the Mac Finder or through a variety of Unix command-line utilities that you can reach from within Mac OS X's Terminal window.