Oh, boy. These three words have confused even the most experienced of writers. So thank God for editors!

But for those of us who can't hire an editor to proofread out long-winding Facebook posts, here's a quick and easy guide:

(Graphic: Angry and maybe drunk? woman trying to write a long Facebook post on their phone. Looks haggard)

Thought bubble contains what she's trying to write: So listen hear. I wuz walking from ma Clunkmobile3000 to the entrance of ShopSmartz and this giant famlee wiv lyk 40 keedz wuz in ma way. Their lyk a flok of pigeons all sreamin and braying right they're blocking the entrance. Its like there parents wuz deaf or sumthin!

(Additional graphic: maybe a giant family in a parking lot making a lot of noise)

As you can see, these types of posts are like the cancer of social media .

So let's fix that!

THEY'RE is a contraction of THEY ARE. 

In the example above, it should be 

“They're like a flock of pigeons, all screaming and braying..."

THERE is a position that tells you where something is.

So where was this flock of pigeons of a family?

Right THERE, blocking the entrance to ShopSmartz.

Lastly, THEIR means something belong to someone.

So whose parents were deaf or something?
 
THEIR (the kids') parents were deaf or something.

(Graphic: Same woman, now looking like nobility with Elizabethan collar writing with a quill:

Thought bubble reads: I implore all you noble ladies and gents to listen to a tale of my travails. I was recently walking from my splendid carriage towards my favorite emporium. But alas, my pleasant stroll was rudely interrupted by a family with multitudinous youngsters. Dare I say they're like a flock of peasants braying to their hearts’ content right there in the foyer of the esteemed establishment. Twas like their parents were hard of hearing or something of the sort!