Venice, a city of dreams, a city built on stilts, relies on its waterways for transport and leisure needs. Getting around Venice means using some kind of boat. The famous starting point is of course the romantic gondola. Elaborate, sumptuous, kitsch gondolas line the canals at strategic points around the city.
Expect to pay in the region of 80 Euros for half an hour; this is not a cheap treat, but it is a lovely thing to do. Romantically gliding through the canals, under the bridges, sat on a throne in a gondola is a magical experience. If you are tired of sightseeing by foot, or just looking for a way to get to some of the more unusual haunts, a gondola trip is brilliant.
The gondoliers are highly trained to guide the gondolas smoothly through the waterways without crashing or otherwise causing problems. They know each other - it's a select band of men, and will greet each other as you cruise, and as they croon.
The guides will take their cue from you. If you want history, then they are extremely knowledgeable and will talk to you about the places you see. A few tall tales are likely to creep in, but that's half the fun too. If you want quiet, say so, and they'll leave you to enjoy your ride in peace.
There are lots of places around Venice where you can pick up a gondola. The Grand Canal is obviously the most popular place, and so you might find queues. Have a look through some of the back canals and you will wait much less, and they're bound to take you onto the Grand Canal as part of the tour anyway.
A water-bus (vaporetto) system also runs around Venice. These are much larger boats so they can only operate around the city edges or along the Grand Canal. They are useful for visiting the islands, and a trip along the length of the Grand Canal is a staple part of a tourist's itinerary. Look out for the frequent yellow stopping points. Timetables are available here. You can buy individual tickets from 8 Euros, or a pass which gives you general use of the vaporetti for a specific period of time (e.g. 24 or 72 hours).
Getting across Venice, quite frankly, is quicker on foot, but sometimes time is not the issue, and a gentle cruise around the city is enjoyable in its own right. If you are trying to get somewhere in a hurry, particularly to the airport, then you can hire a private water-taxi, but in general the frequent public services should be good enough.
If you do head out to the islands, then boats of other kinds start coming into view. Alongside the gondolas are rowing boats, fishing boats, and the other boats which mark out island life. Moving on water in and around Venice is necessary, but also wonderful.