there

1. Most of the time, there means “at that place” (the opposite of "here").
   • I went there to meet my brother.
   • I found my wallet over there.
2. When placed at the beginning of a sentence, there often has little meaning other than "something exists."
   • There are ghosts in that haunted house.
   • There is an old house on the corner.

their 

belongs to them

• All of those kids with their contagious laughter really made my day.
• They didn't want to see all of their hard work go to waste.

they’re

"they are" or "they were".

• They’re going to a party tomorrow.
• You should meet my work friends; they’re a real hoot.

1.