The longest of these (they're) is the easiest not to get wrong. The apostrophe indicates that a letter is missing, in this case a:
They're = they are
Their is a possessive word that shows ownership of something.
There is a word with many uses, indicating a place or position.
In this example the word there takes two subtly different meanings.
QUESTION: Can you see what's wrong with the wording in the photo above?