OS X is built on top of UNIX. The application Terminal takes you from the outer world of OS X to the inner world of UNIX. Terminal is located in the Utilities folder inside the Applications folder.
To open Terminal, double-click the Terminal icon, and you see a window like the one shown in the figure. The window is labeled Terminal — bash — 80x24.
Here’s a rundown of what you see in the Terminal window:
The last number indicates that the window holds 24 lines, each 80 monospaced characters long.
Drag the lower-right corner of the window and you can make it bigger or smaller.
The word bash in the window label is the name of the UNIX program attending you, something that the UNIX world calls a shell. It’s much like the Windows XP command interpreter, cmd.exe.
The $ character in the Terminal window is the bash prompt — Windows uses a right-facing arrow (>) for its prompt. Type anything at the prompt. Press Return and the shell program — bash by default in OS X — tries to carry out your wishes.