All player housing has hooks that can display a wide variety of items. Some items will only go in a particular type of hooks, like a floor hook or a wall hook. To see the hooks so you can open them use @house hooks on. To turn them off again, use @house hooks off. A spell casting item can only be used when the hooks are off (this has always been somewhat buggy, you may need to turn hooks on then off again sometimes for it to work properly).