Their, there, and they’re sound the same, but they have different meanings and uses.
- Their shows that something belongs to or is connected with people, animals, or things. It usually comes before a noun: The neighbors painted their fence. It can also refer to one person: Sam brought their laptop.
- There can identify a place: Please leave the package there. It can also introduce a statement that something exists or happens: There are three messages for you.
- They’re is a contraction of they are. The apostrophe shows that letters have been removed: They’re preparing dinner. You can check this form by replacing it with they are. If the sentence still makes sense, they’re is correct.
Compare the words in one situation: The musicians are over there with their instruments, and they’re ready to perform. Here, there identifies a place, their connects the instruments to the musicians, and they’re means they are.
When proofreading, first test whether they are fits. If it does not, decide whether you need to show a connection or refer to a place, existence, or event.