Привет, Тициана! "О" pronounced "o" when it is under stress. In other cases it sounds like "a"

http://www.study-languages-online.com/stress-reduction.html a short article about vowels reduction. http://www.study-languages-online.com/russian-reading.html - a whole section with some reading excercises, where you can also listen to how the words sound Google translator may be useful if you want to hear how a word sounds. Please find another link to the online dictionary. They outline the stressed vowel in red and you can also listen to the word. Hope that helps.

"Меня зовут Тициана". O is read like A in unstressed positions. E.g.: молоко’ (milk) - the last O is stressed and it is read like O. The first and the second O are not stressed, so that is why we pronounce like [malakO']