Grammar 101 with ShowNoFear
They're - They're is a shortened version of They are, note the '. This is often used when discussing groups of other people.
Oh yea, that mob of ferrals, they're just over at the Kato Cafe, just left a minute ago.
There - There is used when discussing something involving a Location. Note the 'here' in There, 'here, there and everywhere.'
He's running! Over there!
Their - This is used to denote possession. Credits to Yankee for correcting me.
Antlions are coming! Their mouthparts are very sharp!
You're - Same deal with They're. This means You are.
...You're a real dick, you know that? You didn't have to get me this!
Your - Used when addressing something involving the individual you are talking too.
Hey, did you get your books back?