You'll want to leave via the International Gateway - that is a regular entrance to Epcot, so you do need to get your hand stamped. You can also re-enter Epcot there.
You'll want to walk straight to the Yacht & Beach club.
Beaches and Cream is between the Yacht and Beach clubs - at the back of teh pool. It can be a little hard to get to. I don't know if you can get to it through the lobby directly; what we usually do is go into the lobby of the Beach club (it's the first one on your right), and walk by the windows next to the pool (you'll see diners in the Cape May Cafe). We go as far towards the Yacht Club as we can, and exit the building; you should see Beaches and Cream in front of you. You might have to wind around a little bit to get there (sometimes its easier to go through the pool area, but sometimes they won't let you do this).
If you get lost, just ask any CM how to get there.
They have GREAT burgers and even better ice cream! This is my one must do thing while we're at WDW.
