You can use your pass only in countries you purchased on the pass. In your case, if you travel through Switzerland from Germany into Italy, you can use it on valid days in Germany and in Switzerland, and between Switzerland and Germany. You cannot use it to enter Italy, so depending on your route you could use it for a day from wherever you have started in Switzerland (or Germany if all in one day) as far as the Swiss/Italian border - probably either Domodossola or Lugano and you will need a ticket from there to your destination in Italy, probably via Milan.
If you start your journey to Italy in Munich, Nuremberg or other more eastern part of Germany you may well want to go directly south from Munich to Italy, especially if you want Venice, Verona or eastern Italy, or continuing south towards Florence or Rome. If you want to go south from Munich the trip will probably take you to Innsbruck and over the Brenner Pass which is on the Austria / Italy border. That will mean that you can use your pass as far as the Austria border, either Kufstein or Salzberg, and then you will need an Austrian ticket to Italy and an Italian ticket for Italy, or you may be able to get a through ticket all the way which accounts for whatever pass you may have.
Is this a hypothetical question - if so it is likely that we can tell you ways to travel which are cheaper, and in many cases much much cheaper than a railpass, if you will share your itinerary and travel dates with us - or have you already got the Eurailpass and want to know how far it covers or how to add to it?
When is your trip, and what trips are you taking?