Do you mean the Present Perfect tense? There are some good explanations with examples here http://www.englishpage.com/verbpage/presentperfect.html In general, it is used to talk about something that happened in the past but you don't say exactly when, For example; Have you seen this film? Yes, I've seen it. No, I haven't seen it.

http://usefulenglish.ru/grammar/the-key-to-the-present-tenses

I think perfect as adjective may use to express how much someone's actions or behaviours reached perfection. It may be equal in meaning to best, accurate, exact, absolute and so on ...