If you're actively doing anything in any of your apps, finish doing it (e.g., save your progress, or finish sending your email) because we're going to be exiting all of your apps. When you're done, proceed to the next step.
Fully exit from all of your apps by following these instructions. Those instructions cover exiting a single app, but you should do it for all apps.
Fully power down your device. On most devices this involves holding down the Power button for a while, then taking some action on the screen. E.g.:
Clicking a Power Off option (some Android devices)