Many people who arrive at D-FW for the first time actually think that they are in Dallas. They are, perhaps, technically either in Fort Worth or Dallas depending on where they are standing at the monent; but they are many dozen miles from either city center. You have a variety of choices for way of departing this HUGE airport. Taxis, hotel vans, buses or renting a car. You must either through the North Airport Exit or the South Airport Exit.
If you are driving, be sure to get a map and a few directions to get you on your way. In the best of times you have about a 30 minute drive to either downtown Dallas or downtown Fort Worth. During peak traffic hours, a lot longer. A good investment if you are renting a car, is to get one from Hertz that has a GPS system. Well worth it! Of course, when you return to the airport, allow plenty of time as the property is bigger than you think. The distances are longer than you are used to and the signs usually confusing. Sorry, but in over 20 years, they still haven't smoothed out the confusion.