It is about a ten minute walk from the Contemporary to the Magic Kingdom entrance. When you exit the Contemporary turn right. You will walk past the bus station and continue along this sidewalk all the way to the MK entrance.
To walk from the MK to the Contemporary, head left after leaving the MK's gates. Walk toward the bus stop and just keep on going. There is a sidewalk until you cross the street. At that point you'll be in the Contemporary's parking lot.