So, as I see all of these spelling and grammar errors far too often, I feel compelled to put a helpful page together.

I hope this clarifies the offending spelling and grammar mistakes!

their = belonging to them. eg Their server.
they're = they are. eg They're losers.

it's = it is / it has. eg It's silly.
its = belonging to it. eg Look at its flashy lights.

you're = you are. eg You're an idiot.
your = belonging to you. eg Your spelling is atrocious.

loose = not tight. eg You have a screw loose.
lose = not win, the act of having lost. eg I think we're going to lose.
loser = the one who lost. eg He is such a loser.

who's = who is / who has. eg Who's an idiot?
whose = possessive who. eg Whose grammar is atrocious?

Too = excessive. eg This is too confusing.
To = opposite of from. eg This is going to kill me.

desert = sandy. eg We were crawling through the desert, sand getting everywhere.
dessert = yummy. eg We were crawling through the dessert, until the waiter stopped us.

affect / affected = verb. eg Brain damage affects you. I was affected by it.
effect = noun. eg The effects of the brain damage.