I would like to understand the function of "з" in "зробили". Could please someone explain this to me? thanks. As I know "робили" means to done, for " second sing. person, and plurals". From the sentence what I can understand is "the action has been completed. but isn't "робили" itself means to complete the action already?
'We did it!' is another variation. In the perfective aspect of Ukrainian, completed actions are defined, so 'we have done it!' and 'we did it!' are included. In simple terms, the perfect aspect in Ukrainian does not match the past perfect tense in English, but covers the past simple and the past perfect, as both deal with completed actions in the past. This is confusing at first to English speakers. Again, to simplify, the imperfect aspect covers the two continuous tenses. There are other ways in English to refer to events in the past (and the future!), using time related words and the present tense, but this is a subject which is probably outside the usual scope of Duolingo and this discussion.
Зробити is a synonym of Виробляти, so the answers "We have made it!" or "We created it!" should also be accepted.