In case you just upgraded your iOS powered device to iO7 or any other version and now this device runs slower than it used to, this resetting of the device procedure might speed things up.
If your phone doesn't want to boot up again after the update, it gets stuck in a black screen, follow this tutorial where we root the Galaxy SII with Odin and put an official Samsung Android 4 ICS on it.
Airplane mode on a phone is when you disable all the active connections like WiFi, bluetooth and mobile network. Let's see how to enable it so you don't need to turn off your phone on an airplane.