2.0L = volume air the engine displaces from the top of the stroke to the bottom, x the number of cylinders or pistons, in your case 4.
Dual Overhead Camshaft means the valves that let air (and fuel) into and out of each cylinder are controlled by a camshaft rod above the cylinders, in the head(s). Each bank of cylinders had two camshafts (dual).
The Zetec (Ford's name for it) is a very good engine, but most people think it's a little small for the Contour. As mentioned, check out the Zetec forums for detailed information.
