Most common problem we see on an iPhone is the black screen but it can also be an issue on iPads. If the black screen problem has happened to you the first thing to try is a reset. If its not that you may have a broken screen, bad chip on motherboard or a bad battery.
On i6S and older hold the power button and home button at the same time.
On i7 or 7 Plus hold power button and volume down button.
On i8 and above its a little tougher. Click down volume one second. Up volume one second. Click and hold power button until it resets.
On all of the above you will see the Apple Logo if successful.