In settings/power untick fast boot
turn your device off
hold vol down, click power
information you want will appear on screen (among other things)
Then you will be able to reboot device. You move trough the menu on vol up/down, and you select option with power button. DO NOT pull battery out, or some similar stunt. Navigate to "fastboot", click power, then in fastboot menu navigate to "power down", or "reboot" and click power button.
There is no need to perform backup before this because you make no changes to your device..
If you decide to root/install custom rom you have to do MUCH reading before doing so. Make sure to educate and be sure in what you are doing before trying ANYTHING with your device, because you can and will brick it if you don't.
And make sure to search before you post!