If you are an EU citizen you don’t have to request a visa.
If you are a Non-EU citizen intending to enter Italy you must submit your visa application and the relevant documents to the Italian diplomatic representation. The visa procedure might slightly change depending on the Embassy/Consulate, they however all require the reason and duration of your stay as well as the proof of adequate economic means and accommodation. Therefore we suggest you to query the Italian Ministry of Foreign Affairs website: by selecting your nationality, your residence, the length of your stay in Italy and the purpose of your visit, the database will give information about the type of visa and the documents required for the application.
Once arrived in order to legitimate your stay you must submit your stay permit request to the Immigration Office within 8 working days from your arrival.
In the attached document you can see which kinds of Visa you can request.