The Italian Ministry of Foreign Affairs provides two different websites to help foreigners getting the right visa: an easy one, with basic information (which might be enough for a large number of visitors), and a more comprehensive one, with all the relevant information.
Please be aware that the Italian Immigration Law has been designed to prevent citizens of most of the countries listed on this page from legally entering Italy, which makes the tourist visa the only available choice (unless you are willing to leave a substantial deposit in Euro to the Italian embassy of your country of origin).
We are happy to help you by sending you an invitation to the conference, but this will not help at all if you are a citizen of one of the aforementioned countries. Also, please be aware that current relationships between Italy and India make the process incredibly complicated for any kind of visa (apart from the tourist visa). Please send an e-mail to email@example.com before applying for any kind of visa.