If you are staying in Venice and the weather is nice, tour Venice on foot. You'll almost certainly enjoy walking through the narrow alleys (calli [sing. calle]) of this enchanting city. You'll come across many little squares (campi and campielli), small shops, as well as stands selling souvenirs of many kinds. Beware: Do not buy merchandise from the street sellers with their wares laid out upon sheets. They are usually not Italian, are irregular, and much of the merchandise is counterfeited (accessories: purses, belts, glasses, wallets, etc.) for which the purchaser can be steeply fined (+€+1000s!).

Being located on a collection of islands in the middle of a lagoon, there are times where you will need to use water transportation to get from one place to another. Venice has a very efficient public transportation service run by the public company ACTV, based mainly on various sized "vaporetto" boats ("water buses"), which derive their name from the time long past when they were powered by steam engines.

Vaporetto lines run on a schedule and guarantee essential connections to outlying islands such as the Lido, Giudecca, Murano, Burano, Torcello and others throughout the entire night as well.

For more information about Public Transportation, with details about fares and routes check the links below:

Vaporetto route map

Vaporetto timetable

Vaporetto fares

Vaporetto route descriptions

or consult the TripAdvisor page which has a section dedicated to fares and passes.

Connections to and from Marco Polo airport are run by a different company - Alilaguna - with specific lines and fares.

For Cruise Passengers - there is a "People Mover," a shuttle train that runs directly between the Stazione Marittima - the cruise port - and Piazzale Roma. It only costs 1.30 Euro each way and runs frequently.  

However your cruise liner may be moored in Stazione Maritima some considerable distance from the People Mover so if you have a lot of  luggage you may well be advised to call a land taxi which can either take you to Mestre railwaystation on the mainland, or take you direct to Marco Polo airport if you are not spending time in Venice or direct to Piazzale Roma if you do intend to spend time in Venice.  From the landing stage at Piazzale Roma various water bus lines serve most of Venice, the Lido and some of the surrounding islands in the lagoon.  Alternatively, as all the remainder of Venice is pedestrianised, you can walk if you wish, into the more interesting parts of Venice though it can be quite a way if you are carrying or wheeling your luggage.