Yes, You have came to the right place..
You iPhone has shut off. (Just gone to a black screen) That might be caused from a lot of things in the iPhone its self. But ill tell you how to fix the problem.
You will have to do a hard reset on the device. (You will not loose any data on the Phone)
Just follow these couple of step's an the Phone should be back in working order..
1.Press and hold home button an the Power/lock button at the same time.
2. The Phone will shut off.. But please keep holding them buttons in.
3.When you see that apple logo appear please let go of them buttons.
(*PLEASE REMEBER KEEP HOLDING THEM BUTTONS UNTIL YOU SEE THE APPLE LOGO*)
Robbiee. 🙂