In the game a key mechanic is summons or summoning, In which you can summon all sorts of creatures to fight for you.
Location: You equip and unequip summons in the inventory menu, and you can see what summons you have above your health bar, and your SP points are to the left of them.
How To Use: When you hit an enemy you gain Sp points or Summon Points. Which you can check how many you have on the left of your summons. When you have enough Sp you can summon an ally to fight for you, you will know you have enough Sp when the summon icon glows. You can also check the Sp requirement in the summons description in the inventory menu.