There - their - they're

Learners of English often confuse 'there' 'their' and 'they're'. 
These words have the same sound but not the same meaning.
The explanation and examples below show the differences between them.

THERE

• There is the opposite of 'here'. It means in that place, not here.
  • Where is my pen? It's there on the table.
  • I'm taking the train to London. I'll call you when I get there.
  • You can park there beside my car.

• There is, there are, are used to indicate that something exists.
  • There is a cat in the garden.
  • There are many cars on the road.

THEIR

• Their is a possessive adjective just like 'my' 'your' 'his/her/its' 'our'.
  It is used before a noun and means that something belongs to 'them'.
  • Their car is red. My car is blue.
  • They invited all their friends to their wedding.
  • My parents are very pleased with their new house.

THEY'RE

• They're is a contraction of they are.
  'They' is the subject of a sentence with the verb 'to be'.
  They're beautiful = They are beautiful.
  • Where are the children? They're at school.
  • The children are attentive. They're listening to the teacher.
  • People are voting today. They're electing a new president.