if there is nothing else in your model, then global goal force in the Z is your drag force.
otherwise you should use a surface goal, select all the surfaces of your body and use force in the z to get your Fd.
you can calculate your Cd using an equation goal at that point.
if you haven't done so already, check out the tutorials in flow and the technical reference and the solving engineering problems pdfs. there are specific examples of what you're trying to do. also there are articles on it in the solidworks customer portal. just search for drag force.