MaxiMom,
You have to understand that Disney World covers 47 square miles. There are 4 main parks (MK, Epcot, MGM, and AK), 2 water parks (BB and TL) and the DTD area (shopping, DQ and PI). They are not next to each other. they are spread out across the 47 square miles. You can't walk from one park to another.
For MK, if you are driving you park at TTC. If you are not near the fron of the huge parking area you can take a tram to the front. From there you will take either the monorail or a ferry to the MK. For Epcot, MGM, and AK you park in lots near the parks. There are trams to take you to the front gates if you are farther back in the lots. There is also a monorail that runs from TTC to Epcot, but if you are just going to Epcot I'd park in the Epcot lot and not TTC.
If you are staying on site you park at your resort. You can then take Disney transportation to each park. The exact transportation available to go to each park depends on the resort you are at and where you are going to. You can also drive to the parks but you park in the same lots as everyone else. If you stay on site there is no charge for parking.