Today's homophones...
They're/Their/There:
They're is a contraction that means "they are." They're going on the Bsb cruise in December.
Just like with you're, the rule is simple: if you can replace it with THEY ARE, use THEY'RE.
Their, like your, shows ownership. Which one is their cabin?
If it belongs to them, use their.
There is what you use when it doesn't mean "they are" or something that belongs to "them." There can be a place or is used before a linking verb, like is/are. Their cabin is over there. (See the difference?) There are lots of freaky fans on this cruise!