You can use the Buses even the ones to the Disney Resorts, But if you park at Downtown Disney keep in Mind it can take up to an Hour to get to where you want to go depending on the Park that you want to visit.
Most of the time you have to ride the Bus to TTC then
Switch to a Monorail or another Bus, then when its time
to Return you have to ride it back again, also the Downtown Disney Routes To/From always are the Busiest of all Routes at Downtown Disney.
There are ways of getting around Disney, but it will take awhile to learn the System.