Да понимал спасибо очене :) :)

Oops! Something has happened to Italki and you can see my correction in a wrong form!!! So trying to correct that with my comment :))) The difference between these words is an aspect. There are two kinds of an aspect - perfective and imperfective aspects. Perfective aspect means finishing a part of the work or all the work, imperfective aspect means that the work is continuing (kind of English verbs: 'was doing' - imperfective aspect, 'did', 'done' - perfective one). "Знать" - imperfective aspect, "узнать" - perfective aspect; "думать" - imperfective aspect, "подумать" - perfective aspect; "делать" - imperfective aspect, "сделать" - perfective aspect. Look at the examples and compare: Я знал, что русский язык прекрасен - I have been knowing that the Russian language is beautiful; Я узнал, что русский язык прекрасен - I've known that the Russian language is beautiful. As you see - in the first case the sentence means 'I have been ALWAYS knowing' and - the process of knowing is STILL CONTINUING, but... the second sentence means that 'I've JUST KNOWN' and - the process of knowing is FINISHED. I hope you can understand that :)