Dragons can be stored in the hangar when not being utilized on Berk. You can feed Dragons and send Dragons training to the Academy while they are in the Hangar. However, you cannot send Dragons to a Titan Training while they are in the Hangar. The capacity includes 70 Dragons spots without expansion. However, you are able to buy more space with Runes.

 Any Dragon hat is bought, acquired through Collections or Card Packs can be placed in the Hangar even if the Hangar is at its maximum capacity. While the Hangar is full or above capacity, it is not possible to train or feed your Dragon.