You'll get a card to place on your dashboard, identifying your resort and your checkout date. That serves to identify you as a resort guest entitled to free parking in all lots, and long-term parking at your resort (usually you can only park a max of 2 hours at resorts other than your own).
We drive our own car all the time on WDW property and love the freedom it gives us to go wherever, whenever, and not be tied to the buses. The best map of the property we've gotten was from our Unofficial Guide, which had a great pull-out map to make sure we could easily get from place to place (although the signs are pretty good).