Literay helpful pointers

Through my education so far, almost every Teacer I have had has always had the difficulty to clarify theses common mess-ups, even the ones we were taught in second grade. Maybe fifth graders are smarter than us.

It's and Its
It's is a contraption of it and is.
It's the right answer after all.

Its is a used to show possession.
The computer had its power cord unplugged.

Affect and effect
Affect is used as a verb to mean to touch or move.
The bird population affects the worm population.

Effect is tied more closely to results.
The effects from the hurricane Katrina can still be seen today.

Principal and principle
Principal is used when the describing the chief or first.
The principal president of the United States was Washington.

Principle is a fundamental element such as a law.
The principle of not stealing is quite widespread through the world.

They're, there and their
They're is a contraption of they and are.
They're over by the water fountain.

There is used as clarifying the subject.
Over there is the radio.

Their is to show possession.
Their radio is on the shelf.

Hope this can clarify those common grammar mistakes.  If I had these nailed down throughout high school, I could be going to Vandy.  Well, it would make me closer to getting in.