Flash game with server backend?

So through out the years, I've played with flash. I've created small games just for fun, with simples images, simple buttons.. All in all very simple. I wanted to take one more step, make a game that lets one person interact with another. I'm not sure how to take this step though.

I assume I need a backend of some sort, but what and how that would work, I don't know. It'd have to be "real time" some how.

Much much, imagine a game with two rooms. You can walk between these two rooms freely. Now add another person to the mix... How would I go about allowing these two players to see each other? It'd have to be "real time" to update a player entering a room and the other player seeing them.


Anything advice or help in the right direction would be of great help. I'm willing to learn.

Not an expert what so ever, but you need a communications server similar to those used for chat.