Italian is spoken primarily in Italy and the Ticino region of Switzerland. There were many Italian immigrants to South America as there were to North America, so there are still Italian speakers in places like Argentina, though of course they speak Spanish, too.
Italian, like French and Spanish, is a Romance language, not a Germanic language, so Italian and German are not linguistically related. They belong to different language families. A native German speaker would not be able to understand Italian without having studied it, though of course many German speakers do study other European languages.
I have studied German, Italian, and French and speak all three, but although having studied French helped me learn Italian, neither French nor Italian was particularly helpful with German. (On the other hand, I'd studied Latin, the parent language of French and Italian, and Latin WAS helpful with German because both Latin and German are inflected languages.)
Edit: If you grew up in a German-speaking region that borders Italy or the Italian-speaking region of Switzerland, you might well pick up Italian, but not because you spoke German. It would simply be a matter of exposure to Italian.