yung, yun

Can someone explain the use of yung and yun,I'm having trouble with these.I read that yung means iyong but it doesnt seem to make sense when I see it in context.This is assuming that yung means "your"the same as iyong.And I have no idea about yun.

Also,I'll just add these other questions instead of starting another thread;why is kung placed before some words,for example,kung ano and kung bakit? Lastly, what does bakit mo ako mean? I know the literal meaning is" why you me?" but it sounds...

yung, yun