One of the peculiarities of Venice, in addition to its history and art, is that all transportation occurs via water or on foot. Therefore, all movement of people and goods is provided by a network of public and private vaporetti (waterbuses) and boats, including:
ACTV, which operates not only the vaporetti but also transportation by land to Mestre and Veneto;
Alilaguna, for the service to and from Marco Polo Airport (and more);
Water taxis
Here are some useful links (there are also apps on smartphones):