Homophones are words that sound the same but are spelt differently and have different meanings.
'Their', 'they're' and 'there' are homophones that often confuse people.
‘Their’ means it belongs to them, eg "I ate their sweets."
‘They're’ is short for 'they are' eg "They are going to be cross."
‘There’ refers to a place, eg "I'm going to hide over there."