Everyone who has a Morale/Magic/Power pool has an initial amount and things which charge or drain it. Things which drain it are often a rolepower, like:

Night Kill: (Y) You can [blah, blah, brutal homicide, blah]

The Y indicates the amount of morale drained per use. You ca not go into the hole either, if something cost 2 points and you've got 1, no use. There are items and events through out the game that can add to someone's pool.