In general terms, as soon as you enter the WDW district, just follow the road signs since they are very acurate to navigate in this magical world.
Since you don't say where are you coming from, I will give you some general instructions.
To go to FW, just follow the same route as if going to MK. As you get closer to MK parking pay booth, make sure to move to the right lane (the one WDW use) and tell the CM that you are going to FW.
Although, I showed them a copy of my reservation, I don't think you shouldn't have any problem if you let them know that you are going to the restaurant. Keep driving to your right and follow the small turn and you are on your way to the entrance of FW.
As soon as you see the FW and Campground sign, make a left and tell the security person the purpose of your visit. You will be advised to park your car and take the internal bus to go inside because there is no parking space inside the fort, except for those staying at the campground (1 car) and a 15 minutes parking time for those who are shopping in the general stores.
There are maps in the bus stops and you only need to take the color coded bus where you want to go.
FW is a very beautiful and relaxing place and people should set apart time to enjoy without time limits. At the marina, you can take a boat to go to Contemporary, WL (nice looking resort), and MK.
Hope this help!