"YOUR" and "YOU'RE"

"Your" indicates possession. "You're" is a contraction for "you are." Ex.: Is this your umbrella? You're a wonderful person.

"PRINCIPAL" and "PRINCIPLE"

"Principal" refers to a person in a position of authority or the primary part of something. "Principle" means a fundamental rule or belief. Ex.: The school principal addressed the students. The principal reason for our success is teamwork. Honesty is an important principle to uphold.