Use the "Shut down" from the Apple menu (top left corner of the screen) or hold the "On" button down for 3+ seconds, Janie. And, if you want to use Windoze (installed alongside OSX in Bootcamp mode), when you start up, hold down the Option key (called the Alt key by Windoze users) as soon as you hear the Mac chord; you then are given the choice of operating systems.

Cheers, Rowan