You can launch Terminal by double-clicking on the icon in the Finder,
or if you have the Terminal icon in your Dock, by single-clicking on
that icon.
Once launched, Terminal may be configured as most Mac applications
can: by setting preferences in the Preferences dialog and choosing a
font family and size from the Font menu.
One big difference between Terminal and other, X-specific
applications is that instead of running individual instances of
xterm, you run one instance of Terminal and may
have multiple windows, known as
"shells," which may have saved
settings (such as color, size, font choice, and various other
settings). You can't run a shell in Mac OS X without
running Terminal.
-- SJC
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3. Setting Up Your Unix Shell |  | 3.3. Shell Setup Files -- Which, Where, and Why |