In general, the studio monitor ideally presents your audio material to you with accuracy, so you know what you "really" have. Naturally this is a subjective area, so i suggest reading my article on the truth about studio monitors to get a good grasp.
Active monitors have have a power amp built right into them. Usually, these are mounted on the back. "Regular speakers" which are also called passive monitors, require an amplifier to drive them. The idea behind active monitors is to match them to an amp which is ideal to drive them. This takes some of the guesswork out of buying a monitoring system. Also, since active monitors are connected directly to your mixing board or audio interface, they eliminate speaker wires and hence another source of potential trouble.