Closing the door to a pocket hideout from the inside causes it to become camouflaged on the outside. You can retrieve the door as an action by speaking its command word while the hideout has no creatures inside it. When you do, it shrinks back down to its replica size.
Rarer pocket hideouts feature additional benefits such as granting finer control over the hideout's layout, responding to commands while you are inside, and the ability to alter its atmosphere.