On the iPhone, double tap the home button to see all currently running apps. If you want to close an app, just swipe up on the app window. If you want to open a recently visited app, just scroll to the left or right and tap the app you want.
15 Things You Did Not Know Your iPhone Could Do. Did you change your mind about that text you just tapped in? Shake your phone, and an “Undo Typing” box will come up. If you change your mind shake it again and a redo typing box will pop up