Their is the possessive pronoun, as in "their car is red"; there is used as an adjective, "he is always there for me," a noun, "get away from there," and, chiefly, an adverb, "stop right there"; they're is a contraction of "they are," as in "they're getting married."

What is an example of they re?

They're is a contraction that is defined as they are. An example of they're is what you say when expecting guests and the doorbell rings, “They're here.”

When to use they are vs they re?

There has the word here in it. There is the choice when talking about places, whether figurative or literal. They're has an apostrophe, which means it's the product of two words: they are. If you can substitute they are into your sentence and retain the meaning, then they're is the correct homophone to use.