Your LP is made up of the LP of these five cards here above your LP meter. These five cards are your Soul Cards.
First is "Standby". When you select a Unit to "Standby", it will heal HP equal to 25% of its MAX HP.
Most units have the options of "Attack" Standby" "Move" and "Iczer Attack" You might not be able to use Standby or Move effectively at first, but when you're more experienced these options will come in handy.
Next is "Move". This lets you move the Unit to a different area of the grid. If you don't want to take a hit, you can move out of the enemy's range.