Double tap the Home button to bring up the iOS Task Manager and then locate the app you want to force to quit. Tap and hold the icon for that app until it begins to wiggle. A red circle will appear with a white minus sign in the center superimposed over the icon. Tap the red circle and iOS will force the app to quit.
I use a MacBook with an external monitor and keep the MacBook’s lid closed. When I want to go somewhere, I disconnect the MacBook from the display and stick it in my bag. But when I open the lid, the MacBook wakes up, and most of the time the icons that were on my Desktop are gone. The menubar and Dock are still around, just no icons. How do I bring them back? I’ve been restarting the MacBook every time, but that takes a while and isn’t so convenient.