The currency used in Italy is the Euro, the same currency used throughout most of Europe.
The euro comes in denominations of 5, 10, 20, 50, 100, 200 & 500 euro notes, and 1, 2, 5, 10, 20 & 50 cent coins.
Each country prints its own euro notes and mints its own euro coins. Every country has its own design on one side of its notes and coins, and a common design on the other. All euros, however, are the same size, have the same value, and can be used in all euro-based countries.
Exchange rates can be found in your local paper and financial website.
You won't need to convert much currency. It is fine to pay for larger purchases, as well as things like meals in restaurants, in Italy using your credit card. The exchange is calculated for you, and at a favorable rate.