You're really means ‘you are’, the apostrophe (apostrophe = ') shows us that the ‘a’ is missing:
"You're really boring. I wish I didn’t have to sit next to you all day.”
Your is a possessive pronoun and should be followed by a noun:
‘Your car, your phone…’
One common mistake is to say, ‘Hope your okay’.
It should, of course, be, ‘Hope you're okay’.
