Hello @Liliane25 ,
it's possible to rent a single room in your house without being a "professional" (which means registering a VAT number in Italy - "Partita IVA").
However, if you plan on renting several rooms, I believe it's necessary to be "a professional", which means you will need to get a "Partita IVA" and communicate this activity to your municipality.
You can find more information about this here (it's an article in Italian, but you can check if you can use Google Translate on your browser):
https://ibpost.it/finanza-immobiliare/affittare-una-stanza-della-propria-casa-a-turisti/