Apostrophes are used to show possession: Mark’s pen, Joe’s house.
If the noun (singular or plural) does not end in ‘s,’ add the ‘s’ and the apostrophe: Mal’s desk; the doctor’s book.
If the noun does end in ‘s,’ just add the apostrophe: Ross’ wife; The doctors’ car.
They can also be used to indicate the omission of numbers or letters: the summer of ’02; they called him Suga’
Don’t use apostrophes with pronouns like ‘his’ or ‘her’ as they’re already possessive by nature.
Also, it’s not recommended to use them with titles of books/movies, or abbreviations.