Real Dictionary

you know
convention: People use you know when they are uncertain about what they are saying or what they are going to say next.
convention: You use you know to emphasize or to draw attention to what you are saying.
convention: You use you know when you are trying to explain more clearly what you mean, by referring to something that the person you are talking to knows about.

you know in American English
you understand

you know in British English
a parenthetical filler phrase used to make a pause in speaking or add slight emphasis to a statement