I did that but Russian instead of Italian
To use Italian as your default language on the frontend, and considering your want "example.com/" to open in Italian and "example.com/en/" to change to English, do the following:
As this is a new installation, and you have no real data yet, delete all languages but the default one, of course.
Change the default language title to Italiano
Upload Italian translation files to it
Create a new language, name "en", title "English"
Edit the homepage and set the "en" language as active and the url as "en".