Each spell has its effect. They can increase you energy recharge speed, help to increase your experience level, or prompt best moves on match-3 levels. Tap the Use button to activate the spell. You can also use spells right after you purchase them in the Shop.
You can't use two identical spells at the same time. You can't use more than three spells simultaneously.
You can check your current number of spells of a certain type in your Inventory.