"Your" is used to describe something that belongs to you:
Your house is red.
I ate all of your cookies.
Is that your hat?
"You're" is a contraction of "you" and "are":
You're a fireman.
(You are a fireman.)
If you're going to the store, take me with you.
(If you are going...)
Is it true you're an astronaut?
(Is it true you are an astronaut?)
If it can be replaced with "you are," you want "you're." If not, use "your."
You're going to your bank to see if you're qualified for a loan.
