First I practiced on the V band images, getting used to the program and the process:
Later, I struck out on my own (with Lydia right next to me for support) to reduce the I band images. I made a beautiful master flat:
Due to variations in pixel size, dust grain in the optical surfaces and more, even if there is a uniform light source the count level across the image can vary significantly.
The master flat accounts for variations in count level across the image (we subtract the master flat from the science images).
It was a very productive afternoon!