Potions are Collectables just like the Keys and Coins, but since they have an effect when used we had to make a new script for them. In the "Collectable Database" object you will see a Healing Item Collectable Data script. This is exactly the same as a regular Collectable Data script but has a "Heal Amount" property.
The "UI Controller" object references this data in the Combat - Bottom Bar UI script. This is how you use a potion when the potion button is pressed.