Thanks aolander.

To clarify further, I am referring to shooting in the M (Manual) shooting mode of the camera. Using the exposure indicator , after one chooses the Aperture and Shutter speed till the right exposure is indicated ( which as you have explained is based on the ambient light), then how does one predict what using a flash will do ? Wouldn't the light added by the flash result in an overexposed picture?So the question is how does one factor in using a flash while setting the Aper& Shutter Speed.. should it be left at a step or two underexposed so that the flash can then "fill in" the remaining light?