Most likely before you even hit the Magic Kingdom, you'll need to make your way to your hotel to check in. It's worth noting the Orlando International Airport is a bit of a drive from WDW and its resorts. We've tried to lay out your options on how to get to your room from the airport.
Maybe you're familiar with it, or maybe not, but if you're staying at a Disney resort, you can get from the airport to your resort with Disney's Magical Express service. Totally free of cost to you, they'll also take you back to the airport when your stay is over. Even better, the Magical Express personnel will take care of your bags for you and get them to your room so you won't have to lug them around. It might be wise to note, however, that you may be in for a bit of a ride on the Magical Express; chances are slim that you'll be on a bus bound strictly for your resort, and you may be subject to several stops before arriving at your own hotel.
Of course, while handy, the Magical Express isn't the only option in town from getting to the airport to your accomodations. We've tried to include some info in this regard, too, so you can make an informed decision on this important part of your vacation.
A good guide from the Mouse on how to get from the Airport to WDW. Note that they've partnered with a few specific vendors, which are mentioned here. WDWforgrownups.com doesn't have any particular problem with these vendors, but there are certainly other rental car/town car/shuttle bus companies that you should research as well.
Disney's Magical Express service is a free round-trip bus ride between the Orlando International Airport and your WDW hotel. Sign up for the service when you book your WDW hotel stay and receive baggage tags, which will allow Disney to collect your luggage on your behalf and whisk it directly to your hotel room--without your lifting a finger!
NOTE: They pack lots of folks onto the bus with you--who aren't necessarily going to the same resort hotel that you are--so Magical Express can mean a bit of waiting before arriving at your hotel.