"IVA" (pronounced "eevah") is short for "imposta sul valore aggiunto" which means value added tax (VAT). If you will be in Italy to practice an independent activity or profession (such as an independent artist, consultant, author, etc.) and you will want to invoice for your services or products, then you will need a "partita IVA".
To apply for a Partita IVA you will need to take your permit to stay, passport or carta d'identita' and your codice fiscale to your local Agenzia delle Entrate. It is very simple and straightforward. One thing you should do though before applying is to go online to the main site of the Agenzia delle Entrate and find the code for your type of activity.
After registering for a partita IVA you have 30 days to go to your local Camera di Commercio and apply for a business license. They will then help set you up with the other offices (INPS, INAIL, etc.) There is a minimal fee of a little more than â‚?60 to do this. Some businesses do not need a special license so you will be able to skip this part but call first to make sure.
After you have all of this set up you need to get an accountant. Your best bet starting off is with Conf Commercio as their rates are very low and they will guide you through everything.