What is the difference between "their," "there," and "they're"?

"Their" shows possession, "there" indicates a place, and "they're" is a contraction of "they are."

Use "their" when something belongs to a group: "Their car is parked outside." Use "there" to indicate location or to introduce a statement: "Put the book over there" or "There are three options."

Use "they're" only when you could substitute "they are": "They're arriving at noon" means "They are arriving at noon."

If you can replace the word with "they are" and it still makes sense, use "they're."