Foam vs wood is easy--foam is lighter, softer, and cheaper than wood and is usually found in the core of cheaper, beginner oriented skis.
Rocker is not vs camber-- a ski can have both. The most common shape for a ski is tip rocker, camber underfoot, +/- tail rocker. Rocker refers to and upturning of the tip or tail of a ski. Rocker makes a ski easier to turn and tip rocker makes it float better in powder. A full rocker ski is shaped just like the rocker on a rocking chair and is meant for powder. Camber is the opposite shape--the center of the ski is off the snow with no weight on it. Cambered skis are meant for skiing groomed runs and are more stable at speed and hold an edge better. A fully cambered ski is meant for high speed carving and racing on hard snow. These days most skis for general use under a variety of conditions at all ability levels will have tip rocker (also called early rise), camber underfoot, and maybe some degree of tip rocker.