From the Window Start button open the Start Menu. On the right side of the Menu window is a little triangle pointing to the right. Left click on it. This will open another menu. The menu will read Shutdown, Restart, and maybe Log off items. The numbers of items listed in this sub menu will depend upon your computer, number of users, and features that the manufacture has added.

A Side Note: Your should never shut off or restart your computer by unplugging it from the wall unless it is a last resort. Not turning off a computer through the Windows start menu could cause damage to the Windows Vista or the hardware inside the computer case.