Homophones make spelling much harder when you are transitioning between spoken and written English. Native speakers of English mix-up these three words quite frequently, so rest assured that this is challenging for everyone :). The key is to really pay attention to what you are writing in order to prevent this mistake.
There is used to specify place.
e.g.: I parked the car over there.
There is also used to talk about the existence of something.
e.g.: There is milk in the fridge.
Their is a possessive pronoun.
e.g.: Their car is parked over there.
They’re is a contraction of they are.
e.g.: They’re not going to use our car. They’re going to use their car which is right over there!
If you need to use the word there, remember that there is here with a ‘t’. There is usually used to talk about a place, so making sure here (a place) is inside there (usually talking about a place) might help you remember the spelling!
They’re is a contraction of they are. When you are reading what you have written, to make sure it is correct, say ‘they are’ out loud. If it doesn’t work in the sentence, then you know you have used the wrong spelling.
Their has “he” and “I” in it. These are pronouns that refer to people. Their always refers to people owning something, so make sure ‘he’ and ‘I’ are included when you spell the word!
I hope this was helpful!
image source: theoatmeal.com