When you park at the MK, you first go to the TTC. Most people take the tram. If you arrive fist thing, way before opening, you won't get a tram because you'll be parked close to the TTC. If you go throu with the AAA pass, you'll also be walking to the TTC. If you can tram it, do that the first time.
When you arrive at the TTC, there are two ways to get from there to the MK. You can take the ferry, which goes ONLY to the MK. You can also take a monorail. If you opt for the monorail, be sure that you do NOT get on the one marked EPCOT. There are two different lines for two different monorails. The one for Epcot runs to Epcot and back. The other one will take you to the MK. I learned this the hard way the first time I got on the monorail.
It really is much easier than it sounds. And MK is the only park that takes this long and is this big a hassle to enter.
The busses, boats, monorails and ferries at Disney are all free.
If you're in a WDW hotel, you'll get to the MK much quicker and easier by bus. Everywhere else, it is quicker and easier to drive.