CFD

If I would like to calculate the lift and drag for an arbitrary shaped object, how would I do that? It does not have to be very accurate, but fairly realistic would be cool. I''ve read about cfd, but doesn''t understand how it works. You make a grid box around the object, substracts/remove any grid point wich is inside the object. And then for each point, you do what?.. Calculate the air velocity vector at each point and somehow also the pressure, and from that you get the lift and drag for the whole object? I''d like some nice introduction to cfd, I''ve searched but found either to simple or to complex stuff.