Getting Started - Running Android: Using Your Phone and Tablet for Work and Play - page 6

Screen Orientation
Android devices automatically switch from portrait to landscape mode when you rotate the
device (unless you've locked the screen in Settings.) To avoid confusion, all of the screen
descriptions in this topic assume that the screen is in portrait orientation, unless noted.
Lock Screen
Android devices go to sleep and the screen goes blank after a short period of inactivity,
which greatly extends battery life. The device goes to sleep even if it's on a charger, because
it charges faster with the screen off.
Most Android devices default to a slide lock screen. To turn it on after the tablet has gone
to sleep, press the power button momentarily, then swipe the Lock icon upward. There are
other lock screens you can set- see Securing Your Device .
Navigation Bar
At the bottom edge of the screen, you'll see the Navigation bar, which always contains three
icons. If they aren't visible, which can occur with some full-screen apps such as games and
reading apps, touch the center of the screen.
The center icon is the Home icon and tapping it always takes you to the last Home screen
you were on. If you have more than one Home screen, tapping Home a second time always
takes you to the main Home screen.
The Back button on the left takes you back to the previous screen that you were using. Tap-
ping it repeatedly takes you back further.
The Recent and Back buttons are your friends. Whether the last place you visited was a
web page, your email, a map, or some other app, the Back icon can take you right back
there. And the Recent button save a lot of time when you're repeatedly flipping between
apps- say from Gmail to the web, or Wikipedia to a dictionary.
Even though an Android device can't show more than one app at a time on its screen, many
apps continue to run in the background, and if you open them from the Recent button you'll
be right where you left off.