To get started, you simply enter your surname in the search bar labeled Cognome: in the top left hand corner and click the arrow or hit enter.
Now if you have a common surname such as Rossi then it probably won't help you much as the map is almost completely covered by circles meaning the name is extremely popular throughout all of Italy and found in 4541 towns. Now if you have a not so common surname such as Baldovini you will see that it is primarily found in Central Italy and in only 16 towns or villages. By clicking on the circles you will get a close up map of the region the name is found in and with the help of Google Maps you might even be able to zero in on the specific towns.
You can also search for your name in the USA using the Gen-US Surname Map which can be really useful if you're trying to determine not only where your ancestors originally emigrated from but to where those with the surname are currently living. Once again using Baldovini we see that there are currently only three states which the name is prevalent in which make up about 10 persons. But, if we translate the name to Baldwin, the American equivalent to Baldovini, it now becomes a totally different ball game with the name being distributed fairly evenly in almost every US state and which represent hundreds of people.