What Is A Sentence

Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions. Evidence suggests, Why do you think that He doesn't know him from his schooldays means that he does know him? It would only have that sense if you added something like In fact, he first met him at …. Analysis reveals, For a non-native speaker like me, I am always wondering how to use you know correctly, as in the following sentence: Alright, well, for example, like on Saturdays, y’know, what I liked to do. Findings demonstrate, I've been thinking that the phrase " already know " is different from the phrase " have already known ". These findings regarding What Is A Sentence provide comprehensive context for understanding this subject.