This may or may not be useful for you, so you might wish to wait a bit first before deciding whether you need one.
To get one, go to the Poste Italiane bringing the originals and photocopies of the following documents:
1. Codice Fiscale (even just the temporary sheet if you don’t have the card yet).
2. Tessera Sanitaria (even just the temporary sheet if you don’t have the card yet).
3. Permesso di Soggiorno (even just the receipts from the Poste if you don’t have the card yet).
As you enter the Post Office door, get a number under the corresponding letter for “PostaPay”, and wait for your turn. At the counter, you might be asked to fill up a form and sign. Pay the debit card fee (€5 in 2016) and whatever amount you wish to load the debit card with. You will be given the PostaPay debit card along with the password and other information in an envelope.