Alright guys, this needs to be done for people who haven't been taught this in school yet.
The Difference Between "Your" and "You're"
Your
Proper usage: "I saw your picture in the thread!"
Note: Remember this - "Your" is usually used for possession. "Your ball", "your friend", "your mother".
Improper usage: "Your a good artist!"
Note: This usage may prompt the response "What about his good artist", because this sentence is implying that you own a good artist. (Which may be the truth, but isn't likely.)
You're
Proper usage: "You're a good artist!"
Note: Remember this - It's a contraction of "you" and "are".
Improper usage: "I saw you're picture in the thread!"
Note: This would read "I saw you are picture in the thread!"