Meanings of You

You mean everything. :-)
Basically, it signifies a listener, but It has 5 different meanings below.

 1. 'You' is a pronoun that indicates a listener. But normally we don't use it for someone who is older than you, because of 4.
😊 당신은 누구십니까? / 당신 누구야? 
- Who are you?

2. Between the married couple, 'You' is an honorific way to call each other(husband/wife).
😊 여보, 당신 지금 뭐 해? 
- Honey, What are you doing now?
(여보 is a pronoun to call husband/wife between marriage couple.)

3. When you're writing, 'You' is a pronoun that calls readers(of the public) with honorific way. You've been read this way in the book titles, magazines or posters.
😊 외국어를 공부하는 당신에게
- To you studying a foreign language

4. When you're argument or quarrel with someone, ’You’ is the dis-honorific way to call the opponent.
😊 뭐? 당신? 너 몇 살이야?
- What? YOU? How old are you?

5. 'You is a very honorific way to call him/herself. We us it instead of '자기(him/herself)'.
😊 어머니께서는 당신이 제일 좋아하는 옷을 입으셨다.
- Mother wore her favorite dress.