THEIR: Possessive of “they“
Their boat needs a coat of paint.
Their website rocks.
Their home is beautiful.
THEY’RE: Contraction of the words “they” and “are” (They+Are)
They’re doing a great job.
They’re hoping for many purchases.
They’re just around the corner.
THERE: at that place or in that place
Now there is a stunning Web site.
Let’s not go there.
While you’re there, take a look at the apple fritters.
ALL THREE IN ONE SENTENCE
Their plans changed, and they’re not planning on flying there.
So there. (Informal phrase used to express triumph, defiance, derision, finality … in this case, it’s finality. Except that the English language keeps changing.)