Kama are the basis of the kusari-gama. Kama is just the sickle on it's own. They are usually used in pairs and swung in various arcs, crescents etc.

All sorts of slashing motions combined with the forward momentum of the ninja they can cause some devastating damage. The blade of the Kama is roughly around 11-12 inches. The handle is slightly longer. Original sickles had a longer blade and shorter handle.