The TTC is the Transportation and Ticket Center. In reality it serves as the parking lot for MK. If you drive you park at the TTC. Depending on where you park you will either walk or take a tram to the TTC (where you can buy tix if you don't already have them). From the TTC you take the monorail or a ferry to MK.
If you use Disney transportation the bus drops you off right at the MK.
You'll find many different opinions on driving vs Disney tranport on these boards. Personally I think buses/monorails/boats are better if you're just going from resort to park and back again. To go from resort to resort, a car is better.
I feel the time with Disney transportation is usually less than driving. With driving most people don't factor in walking to their car (or waiting for the tram, hopping on the tram, driving around the parking lot while the tram drops off other gusts, and walking from the tram to your car); driving out of the parking lot and to the resort, parking at the resort, and walking to the entrance of the resort.
I believe the only time driving is faster is if you've just missed a bus or can't get on the first bus because of the crowds (usually after the park closes). You may have to wait an extra 10-20 mins for the next bus/boat, etc. Of course, if it is so crowded that the buses fill up, how crowded will the trams be and how many cars are trying to exit the parking lot at the same time.
I know many people will disagree with me and tell you driving takes less time. However, I think it's a lot easier to take Disney transportation.