To be admitted to a doctoral programme you must pass the selection examinations as stated in the calls for applications, which are published annually. At least half of the places on offer are covered by scholarships, which are generally funded by the MIUR (Ministry of University and Research), the University, or by external public and private institutions.
General requirements for admission
The suitability of the foreign academic qualifications in terms of content is appraised by the Examining Board constituted for admission to each doctoral programme, in compliance with the regulations in force in Italy and in the country in which the academic qualification was issued, and the international treaties or agreements pertaining to the conferment of qualifications for the continuation of studies.
You can find more details about admissions and scholarships in the University website.