Many Mac OS X application windows such as Mail, Pages, and Numbers, as well as Finder windows, include a toolbar that can be hidden or shown by clicking the Toolbar button in the upper right corner of the window in Mac OS X 10.6 and earlier.
On the top right of a toolbar is the Toolbar button (looks like a gray oval).
If you click this button once, the toolbar icons will collapse and become hidden.
Clicking this button again will show the toolbar icons. You can also choose Show Toolbar from the View menu.
Note: For application windows without a Toolbar button, there may be a "Show/hide Toolbar" choice in the application's View menu.