You only parking pay once per day no matter how many different parks you go to in that day.
If you hit MK in the morning, epcot in the afternoon and mgm at night, you only pay the $9 parking once. You'll get a dated parking pass that you simply show when you drive into the lot of the other park.
If you are staying on property you don't pay parking at all. You'll have a dated parking pass from your resort to show at the toll booth instead.
-m
ps: Please refrain from Posting Like This. It's Really Hard To Read. Thanks.