What Dony said is right, but I wanted to add something: In Korea, it's considered rude/insulting to call someone "당신" The only time this is okay is if it is your wife/husband that you are calling "당신" I'm not sure how to explain why it seems insulting..it just does. Haha. So try not to use this term alot when speaking to others.

Do you have the bag? (=당신"은" 그 가방이 있습니까?) Have a nice day~!