I just want to say that I have developed a new pet peeve - people who do not understand the proper usage of simple and common English words. So I thought I would spell it out, very simply, so we can all understand. ;)

Your and You're
Your is possessive. You're is the conjunction between the two words in the phrase "you are."

• Your mother is so fat she sat on a rainbow and jelly beans popped out.
• You're going to have to figure out how to use these two words correctly.

Weather and Whether
Weather is how it feels outside. Whether is the choice between two options.

• The weather outside is ____ful. (Fill in the blank.)
• I am not sure whether or not you're really understanding anything I'm saying.

Its and It's
Its is possessive. It's is the conjunction between the two words in the phrase "it is."

• The dog ate its homework.
• It's not plain to see whether or not this is making any impact on your grammar skills.

To and Too
To can function both as an infinitive particle used before verbs and a preposition. Too means "also" or "to an undesired or inappropriate extent."

• I can go to school, but it doesn't mean I'll learn anything.
• She can't figure out how to end her book - should the boy marry the girl?
  
• It's time that Americans, too, learned correct English.
• This list is too short.

There, Their, and They're
There is a placeholder. Their is possessive. They're is the conjunction between the two words "they" and "are."

• You should stand there to have your picture taken.
• Their child speaks perfect English!
• They're going to let August Rush into Juiliard!*

Well, there it all is. I hope this has helped your grammar knowledge. It's certainly been good for me to write it. These rules, they're complicated sometimes and their application taxes the mind. Whether or not you're able to use this information, its entrance into your brain will have certainly been helpful. Weather.

*Yes, this has quickly climbed to the top 5 of my all time favorite movies EVER.