If you want your English to sound more natural, make sure you know how to use filler words! They give you time to think of the next thing to say or add flavor to your speech.
You can use this to mean "I think you know," like if you expect the listener knows what you are talking about.
Robin: Who's going to be the best man at Greg and Sabrina's wedding?
Bateman: I think it's Mark. You know, the guy who ate 12 hot dogs at the office party.
Or, you can use "you know" when you want to ask the listener if he or she agrees.
Trevor: You know, I wish that Chick-fil-A were open on Sundays.
Noah: Yeah. I can't get enough of those, uh, chicken biscuit sandwiches!
This is a transition if you are starting a new topic or ending a topic. It's similar to "anyway."
Mark: That Bateman guy always asks me weird questions. So, yeah...I'm going to be to be the best man at Greg's wedding.
Of course you can use "yeah" just to mean "yes" in a casual way, but you can also use "yeah" if you are confirming with yourself if something is true.
Once I was...yeah, I was going to the a water park when I got a flat tire.
Or you can say "yeah" if you are starting to talk about something personal.
My friend got sick, and, yeah, it was a difficult time for us.