Levels 4 and 7 contain the crew quarters. To obtain crew quarters, you can go to the Quartermaster's Office, look at the chart, and then 'rent' some.
They are then to do with as you please - you can 'invite' and 'uninvite' people as you see fit, set the description of the room with 'description'. The quartermaster can also sell you a fine range of furniture. Immovable furniture will be taken to your quarters by our team of dedicated robots. If you wish to get rid of some furniture, try the furniture removal tag.
If you fail to log in for some time (the number of days being either 2 * the number of your rank or 1 week, whichever is greater), you will be evicted from your quarters by the quartermaster. You will be reimbursed for the cost of any items there.
Storable objects can be left in the quarters. They will persist across reboots and crashes.