Foundables in Harry Potter: Wizards Unite are artifacts, creatures or even memories that appear. Casting spells will help you release/acquire those foundables that when returned to the Wizarding World will award you.
The threat level of a foundable is seen on the magical-exposure clock before every encounter. The higher the level the more difficult will be for you to defeat. Each Foundables is connected to a Confoundable, which you have to dismiss to free the Foundables and earn points.
Known Foundables are Creatures (freeing a demiguise who is chained up, using Alohomora, or surviving a Werewolf attack), People (battling Dark Wizards and Death Eaters), Memories (Harry being confronted by the Dementor during the Quidditch match and Ron with a Boggart).