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G'day Jimmy, Flat field frames are images of the flatness or lack thereof of the light coming thru the optical system to the camera sensor. It provides information about the brightness levels (Vignetting) across the field of view, including any shadows caused by dust particles and such. The flat field is not subtracted from the light frame it is divided into it. It is a special form of 'Pixel Math'. Iris can be used to take Calibration frames (Dark, Flat) and apply them to the light frame. The light frame is the actual image such as the one you posted.
Dark Frames are sort of exposures taken with the lens cap in place. In general, though not exclusively, Dark Frames are of the same exposure diration and ISO speed as the Light frame. A more advanced system using Bias frames allows dark frame scaling, but don't worry about that yet.
I see Monte has just replied and replied well, so I see no need to duplicate his efforts, but will just add that IRIS will do all that you want with the possible exception that it might not be able to controll your particular Canera. I don't use Iris myself, but I see under the processing dropdown there are menu items for using dark frames and flat field images.
cheers,
Doug
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