People from certain countries need a Visa to come to Italy.
You can check here: http://vistoperitalia.esteri.it/home/en and if you need a LETTER OF INVITATION, please read carefully the instructions provided in the VISA INFORMATION document.

Check with the Italian Consulate in your country if you need to apply for a VISA. You can check directly on the Consulate official website.
If you need a visa, you will have to apply for a TOURIST VISA (90 days).
Check your passport validity.
Check every document needed by the ITALIAN CONSULATE in your country (every consulate in different country ask different documentation). You can check directly on the Consulate official website. Start as soon as possible!