You can use the Dock, the App Switcher, or a gesture to quickly switch from one app to another on your iPad. When you switch back, you can pick up right where you left off.
Swipe up from the bottom edge of the screen just far enough to reveal the Dock, then tap the app you want to open.
Favorite apps are on the left side of the Dock, and suggested apps—like ones you opened recently and ones open on your iPhone or Mac—appear on the right side of the Dock. The rightmost button in the Dock opens App Library.