Each room looks different because it's furnished by its owner. Graphics in private rooms are twice the size of those in the public rooms to make them cosier and more personal. You move about and chat just as you did in the public rooms.
Many rooms have Stickies on the walls - messages from previous visitors or the owner of the room.
Just click on one to read it. Down at the bottom of the screen, you'll see another icon, next to the Habbo Console. It's a catalogue of all the furniture you can buy to furnish a personal room. It's not expensive, but you pay for it to make your choices more personal - a real expression of your Habbo personality. On the central navigation, you'll see a purse icon at the bottom of the screen.