This one is so common, it makes me wonder if anyone actually gets taught the difference between them by any educator they've encountered since Grade 1.
It's is a contraction of "It is". Use it in casual writing; e.g. It's a great day.
Its is a possessive pronoun. Example: The dog is chasing its own tail.
To summarize, it's = it is, whereas its = its.

This belongs to the same class of errors as it's versus its: a simple mistaking of a contraction for a possessive pronoun.
"Your" is a possessive pronoun used to indicate ownership; e.g. "When your membership expires, renew it online."
"You're" is a contraction of "You are", used in casual writing; e.g. "When you're finished with your meal, please pay at the counter."
To summarize, you're = you are, whereas your = your.