The multitasking bar: You can quickly switch between apps by bringing up the multitasking bar. To do so, quickly double-press the Home button; a bar below the Dock will rise up from the bottom of the screen, showing off the apps most recently run. To switch to a different app, tap its icon.
Multitasking shortcuts: In addition to holding a list of your most recently used apps, the multitasking bar has a couple of other neat shortcuts for your device. If you swipe right, you’ll bring up a secondary set of controls. On the iPhone or iPod touch, you can lock your device’s orientation in portrait mode and control the music currently playing on your device (it defaults to the Music app, but you can also control music from third-party apps). Swipe to the right again, and you’ll get a slider for controlling volume. On the iPad, you can lock orientation, change your device's brightness and volume, and control music.