To place furniture on Avakin Life:
> Open the Edit Mode (icon of a pencil and a chair),
> Drag the item from the bottom panel to the desired location.

The placement will be marked green, if available. If not, it becomes red, and you should just move the item a little bit until the grid turns green.

Have fun decorating!

And if you want to have other Avakins visiting you and rating your Apartment, don't forget to put it in Public mode. 😉