What Eugene said, plus a somewhat shorter (and less informational) answer: The metcons are the ones where you want to puke, and lay around for a while on the floor afterwards.
My current program is: something I feel like doing on Sunday. Monday: O-lift. Tues-Wed. something that makes me want to puke, i.e. metcons. Thur: Powerlifting. Not sure it's the best program, but seems to work OK.