The only ways to get around Venice are on foot or by boat - a vaporetto is the boat-version of a city bus. To get from the Marco Polo Airport into the city, you can take a bus to the Piazzale Roma (least expensive), an Alilaguna boat (somewhat costlier), or a water taxi (very expensive, but perhaps not too bad if split among four people). If you expect to ride a vaporetto much, you might want to buy a vaporetto pass (for 1, 2, 3, or 7 days - otherwise, it costs 7.50 Euros per ride). edited to add that you could also take a land taxi from the airport to the Piazzale Roma, but that would be as far as it could go.