Orc Keys are used to open Orkish Chests in the game. This guide on Where To Find Orc Keys In Return To Moria (Lord Of The Rings) explains where you can find these rare keys so that you can kill all the orcs at the camp, grab the key, and open the chest to claim your reward.
Orc Keys are incredibly valuable as they allow you to progress in the game via fast travel locations and other items using Black Diamonds. These are some of the most vital materials in the early game as it allows you to progress with the story and craft Map Stones, which acts as fast travel locations.
Where To Find Orc Keys In Return To Moria (Lord Of The Rings)
Most of the Orc camps you find, small areas consisting of 3-4 orcs defending a tiny collection of barricades, come with a single chest. After about 15-20 hours, they have yet to respawn, so they are a finite resource. Simply kill all of the Orcs and then in the center of the camp you will see a larger structure, usually with fire on it, a sort of totem-like structure. Simply use your Pickaxe to break the structure and a key will drop. You can then use the key to open the chest.
Save the Black Diamonds. They are very useful.