The attack power (ATK) determines how much damage a unit will inflict on another during an attack move. It can be modified by both the enemy or the player, through spells, unit abilities, items, and terrain area of effect modifiers.
Hit points (HP) show how many ATK points a unit can endure before fainting and being removed from board. HPs are carried through rounds, and can only be regenerated by spells, unit abilities and items.
Movement points (MP) will limit how many board tiles a unit will move before being stuck in place for the next round. Not all tiles will require the same amount of movement points to be crossed, so make sure to plan your movement with care before you start your plays.