Flipping Between Apps on iPad

The Situation

You're using Mail and you click a link that takes you to Safari to view a webpage. Once you're done, you want to go back to Mail.

The Answer:

Using 4 fingers (5 also works), swipe the screen left or right.

The In-Depth Answer:

You can view your open apps by double-clicking the Home button to reveal the multi-tasking bar. Swiping the screen with four or five fingers flips between these apps in the multi-tasking bar.

Bonus Hint:

Swipe UP with four or five fingers to reveal the multi-tasking bar instead of having to double-click the home button.