This one is really easy folks.
Your is possessive. As in it belongs to you. Example: "Your grammar could use some help."
You're is a contraction of the two separate words "you" and "are." Example: "You're going to seem so much smarter if you use them correctly."
If you're in doubt, just ask yourself if the sentence would make sense if you substituted the words "you are" in for your/you're. If they do, it's you're. On the other hand, if you can easily substitute the words "his" or "her" or "my" your choice is"your." Try the substitutions in the examples above and see what I mean.