Easiest way is to take a bus to the MK, then the monorail to the Poly or Contemporary, or you can walk from MK to Contemporary.
Going from resort to resort, you can just take a bus to a theme park or Down town Disney and transfer to a bus to the resort you are going, but its important you make sure the park you go to offers transportation to the other resort. Epcot does not offer bus transportation to Beach Club/YachtClub/Boardwalk Resorts and HS only offers boat or foot transportation to those resorts. Other than that, you should be ok transferring at a park.