The Disney Transportation and Ticket Center is the hub for all things transportation in the park. This includes parking lots, a monorail, and ferryboats that take you to the parks. It also houses a lot of staff to help with ticketing and any issues you may have. This means you’re more likely to find someone who can help you quickly and efficiently here than in the actual parks.
The TTC is also where you go if you are staying at a non-Disney hotel that offers Disney shuttle service or if you’re a guest who is not staying on the property but wants to use a ride share like Uber to get to the park (the shuttles drop off at the TTC). If you want to rope drop Magic Kingdom, the TTC should be open around an hour before the park opens so you can begin your arrival experience.
It is also where you will find the monorail which is a great way to see the resorts along the lake (Grand Floridian, Polynesian, and Contemporary) as well as Epcot. This is not an inexpensive mode of transport, but it’s still very easy to use and will save you a ton of time waiting around at the parks.