When your iPhone malfunctions, a simple solution is to shut it off and turn it back on. This will fix many simple problems, but it won't fix all of them. If restarting does not work, or if your iPhone is frozen and won't shut off, you may need to reboot it. This process forces the iPhone to shut down completely and boot back up, often solving whatever problem you are having with the device. A reboot may also be needed after a large update.
Press the "Home" button on the bottom of your iPhone and the "On/Off Sleep/Wake" button at the top of your iPhone at the same time.
Hold both buttons down until the screen goes black and the iPhone shuts off.
Wait for the white Apple logo to appear on your screen, signaling the reboot has started.