In order to live regularly in Rome it is necessary to have a residence certificate, an official written document attesting your address.
This allows you to have social assistance, issue of documents, registration to unemployment lists, grant of financial benefits, demand for citizenship and driving license.
If you are a EU citizen and you own a house or you are renting it or having it on a gratuitous loan, or you are hosted by someone who is already a resident, you can request the residence certificate at the offices of the Municipality wherein you are living. 
The documents to be submitted vary depending on your employment situation, in any case you have to bring your passport or identity card.
If, on the contrary, you don’t have a house and you are in a disadvantaged situation, you have the possibility to request the fake residence of “Via Modesta Valenti” with the house number corresponding to one of the 15 Municipalities of Rome where you spend most of your time.
In order to proceed with the registration you will have to go to the Social Service of your Municipality.