You do not even need Luna's bed, any bed will do. It just has to be in your house. You will be asked if you want to sleep, select yes and Luna will come to you in your dreams.
It is here you will upload (or update if you already uploaded) your island and get your dream address. This is also where you can enter dream addresses to visit other people's islands as well.
Ah lol. Stupid Isabelle could have least said that on her daily update. She must be back on the drink again.