The Hoard is where every upgrade and resource you find and use is listed. There are no treasures in this game so if you see a man-made item it is an upgrade.
These can make your Pikmin better. Some are good for everyone, while some are only good for one Pikmin. You have to make your decision carefully as once an upgrade is applied it can never come off.
see Pikmin:Redemption/hoard/upgrades for the full list of upgrades.
These can be used to build walls and swords and shields to help defend your landing sites.
see Pikmin:Redemption/hoard/resources for the full list of resources.