The command line is the primary interface to Unix. While there are many graphical interfaces for Unix systems, the command-line interface gives you the greatest control over the system. Furthermore, the command-line interface is virtually identical on every Unix system you are likely to use, from Mac OS X to Linux, FreeBSD, and Solaris. Of course there are differences, but there are far more similarities. Once you learn how to use the command line on Mac OS X, you will be comfortable using it on any Unix system.
A reminder before we go further: Whenever a task in this book asks you to type something, always press at the end of the line unless the task description specifically tells you not to.