When travelling from Resort to Resort, you need to go to a "Hub" and transfer. A "Hub" would be any theme park, or Downtown Disney. Some hubs work better than others, so it's important to think about it before you go.
For your situation, you can take the Monorail to the MK, and catch the bus from there. Or you can catch the bus to the Studios, and then take the boat to the Boardwalk. If both theme parks are closed, take a bus to DTD, and transfer there.
A word of caution... Do NOT use Epcot as a transfer point for the Epcot Resorts.