Okay, youma in a nutshell. Alright, youma are agents of the dark hole, sent to capture human souls. (ryhmes!) If they're caught by a senshi in the act of attacking, they'll usually send out a monster and retreat. When the monster is defeated, it explodes and fades out of existance. When a youma runs out of monsters, they'll usually be scolded by their leader who threatens to kill them if they don't suceed in stealing more souls and defeating the senshi.

Then the senshi must face the youma themself, which is much much much tougher than the monsters. If the senshi defeat the youma, the youma retreats to the leader, only to be killed and replaced with yet another youma. Get it, got it, good.