Use there to refer to a physical or abstract place. Usually, if you can replace there with here in the same sentence, and it still
makes sense, then you are using it correctly.
Examples
"There is an old haunted house."
"We are going over there to eat."
Use they're as a contraction for they are. Usually, if you can replace they're with they are in
the same sentence, and it still makes sense, then you are using it correctly.
Examples
"They're coming over for dinner."
"I wonder who they're talking to."
Use their to show possession, commonly followed by a noun. Usually, if you can replace their with our in
the same sentence, and it still makes sense, then you are using it correctly.
Examples
"Their dog is pretty awesome."
"Have you seen their new store?"