Behind the Carriage House (the main building housing check-in, the restaurants and resort shop) is a path which takes you from the boat dock to West Side. It brings you in next to the House of Blues and Cirque du Soleil, skirting the water's edge to one side and the car park to the other. If your aim is to get there as quickly as possible, cut across the car park which is normally empty.
The other path runs parallel with the water's edge along the front of the resort (i.e. facing Downtown Disney), eventually taking you out onto Buena Vista Drive and into Marketplace next to the bus stop.