This is a slight departure from my usual subject matter, but I couldn't resist from writing about this.
I'm not a completely intolerant grammar-nazi, but when it comes to a mistake as simple as using the correct version of your/you're or there/their/they're or even to/too/two, I will not tolerate it. These kinds of mistakes are what you would expect from a 9 year old. If you do not know the difference by the time you're twenty years old, you've missed something important. You've missed learning the ability to communicate your ideas effectively to other people. English may be a mildly confusing language, but by ignoring the established rules and using incorrect words you're not making it any easier. There is a reason we have different words for all these things, because they all mean different things and are used for different purposes.
I'll give a guide to using these very simple words below.
A form of the possessive case of 'you' used as an attributive adjective
Your jacket is in that closet. I like your idea.
Contraction of 'you are'.
You're a dumbass.
Refers to a location.
Let's go there for dinner.
Contraction of 'they are'
They're all dumbasses.
A form of the possessive case of 'they' used as an attributive adjective, before a noun.
Their cat smells like poo.
Used for expressing direction or motion or direction toward something.
Let's go to the beach.
I'm coming too!
The number 2.
There are two kinds of people, the ones who understand english, and the ones who don't.