Sorry, I should have been more specific: power cycle means to turn off a device completely (not just put it to sleep), and then restart it. On an iPad you hold down the power button until you see a slider that tells you to swipe to turn off the device. Wait at least a minute for it to finish powering down. Then press the power button again and hold it for a few seconds; you should see a white screen with an Apple logo as it starts up.
On the iMac you can pull down the Apple menu in the upper left corner, and select Restart to power cycle (make sure you have saved your work first).