One of the many confusing things about the English language is that many word choices sound the same. Take the ones shown above – there, their and they’re.
Spend a few moments and commit the following to memory. Then, anyone who reads your work will no longer groan when they see your mistakes.
“There” means a –
1) Place. I put the book there.
2) A point in time. Begin there and continue until you finish.
3) A way to start a sentence or clause. There was no reason to dawdle when he was late.
Their – When you are talking about ownership, you mean their. It was time to return their book since I had kept it for weeks. Their friends, their dog, their project, etc.
And, finally –
They’re means “they are” – the apostrophe shows it is a contraction.
If, when you use “they’re” you can substitute “they are” and the sentence makes sense, you have the right choice. They’re the ones who arrived early.
There, there (another use of “there” – as an interjection to console people) – You can get this right!