Just to clarify, the Fort is so big it has bus connections at two ends, the Outpost end (the main check in area and also where the trail ride area is and the DTD bus connection) and the Settlement end (down by the beach, boats to Contemporary or Magic Kingdom, bus to Wilderness Lodge). Three different internal bus loops run within the Fort between Outpost and Settlement (Yellow, Orange, Purple).
From DTD, the busses generally run about every 20 minutes <supposedly>. They will run you to the Outpost area where the main checkin building is. There is a big parking lot beside it and behind it is the bus stop where you will be dropped out from DTD and the internal busses stop here also. The horse corral/barn for the trail rides is immediately behind the Outpost bus stop. You can clearly see the horses and the smell of "horse" will get you ready for your ride/walk. This is where you will check in.
Bama Ed
PS - the area in the middle of the Fort is the Meadow area where the big Trading Post is, the Bike Barn, the pool, and the campfire singalong/movie area. So the three main areas are Outpost and Settlement on the ends and Meadow in the middle.