Apostrophe -is a punctuation mark. In English, it serves three purposes: When one omits a letter (contractions like don’t). To make something possessive (as in the cat’s whiskers). To make letter plural (as in P's and Q's).
There Naming a place, a thing, or the existence of something Their Showing possession They’re Combining the words “they” and “are” Replace “they’re” with “they are” Cheat Sheet for the Usage of There, Their, and They’re