Hi - we do not "meet," words in English. To describe a new word or expression that you have become aware of you could say: a) I have discovered a new word or expression. b) I have become aware of a new word or expression. c) I have encountered a new word or expression. d) I have come across a new word or expression. d) is the most native way to express this in England. It uses our phrasal verb "to come across," which means to encounter something - for example: "I came across an excellent new restaurant last night," would mean that you discovered a really good new restaurant last night.

Hi! Basically, the two is quite the same, but "Don't you worry" is used to emphasise on the "you", to tell that "you", the person it being said to, to not worry. It's just to stress the word. It means the same. :) Hope this helps.

I'd say that the addition of 'you' makes it a colloquial spoken expression. It's meant to be comforting.

the addition of the "you" is less common in my experience. Since this is often spoken to just one person the "you" is not needed