I know this has been done a million and a half times but I feel like I should contribute something to both the writing community and my generation.
So, I will try to explain the difference is the easiest way possible.
"Your" is a possessive adjective, meaning that it is an adjective used to describe possession of an object or person. "Your cookie." Cookie is both a noun and the subject of the sentence and your is describing to the reader whose cookie it is. Though, this is not a complete sentence because it has no verb in it. It's as easy as that.
"You're" is a contraction. Other examples of contractions would be can't, don't, won't. These aren't the kind of contractions that your mother has before she gives birth. It is a combination of the two words you are. "You're funny." You're is a combination of both the subject and the verb. You is our subject, are is our verb and funny is an adjective describing what you are. This, unlike our other example, is a complete sentence.
Was that too complicated? I really hope not. But please, get it right. It takes the same amount of time to do something right as wrong in this case.