Hi
Sorry if this has already been covered.
I am trying to put a selfie into my story. I have got to the point of getting everything ready and characters in position and posing.
how do i make the camera flash as such?
sorry if this is a stupid question.
Are you trying to make the screen flash as if a camera flashed?
You can always use a transition to simulate a camera flash:
@transition fade in white in 0.5
0.5 is half a beat, so it will go quick, kind of like a camera flash-- then when the transition is done, you can show the picture 
Hope this helps