Welcome to Mousebuzz.
As Jen says, the Transportation Wizard is an excellent resource in telling you how to get around WDW. Quite honestly, I am another.
Will you be staying at one of the Disney hotels or will you be staying outside WDW?
Are you planning to go to more than one park in a day?
Those two questions can help us help you.
Disney operates an extensive multi mode transportation system that connects the hotels to the parks and to Downtown Disney (but does not connect the parks AND Downtown Disney). The main mode are a fleet of a couple hundred buses. Added to that are ferries and other water shuttles that connect some hotels to parks or to Downtown Disney, and of course the monorail.
If you are staying at one of the Disney hotels, you can effectively park your car at the hotel and use the free mass transit system. (Most cities in America wish their bus systems were this efficient).