Turning a pronoun into a possessive pronoun is pretty simple, and is often just a matter of memorizing the right word.
He -> His
She -> Hers
Your -> Yours
They -> Their (smaller: Not to be confused with there or they're!)
It -> Its (smaller: Not to be confused with it's!)
Note to graphic artists: Put the text above into a pretty table of sorts, like the one shown below. If you can think of more fun/creative ways of doing this, please feel free to go crazy.
But what about turning a noun into its possessive form? That can be a lot trickier, especially if you're not quite sure where the apostrophe goes.
An apostrophe is a punctuation mark that lets you shorten a word or phrase by using it to replace the missing letters (example: do not becomes don’t), and it’s also used to show ownership of a thing.
As a general rule, you put an apostrophe after the word and then you add s.
The old woman's cackle
A chicken's nest
A literature lover’s favorite place to get drunk
If the word ends in s, you can turn it into its possessive form by adding only an apostrophe.
The cactus' prickly exterior
The bus' ineffective air freshener
Sherlock Holmes' evident scowl
That also goes for plural words that end in s. Simply add an apostrophe at the end of the word.
The cats' distinctive stink-eye
Her friends' backstabbing ways
The Oscars' official engraver
However, you must never ever use an apostrophe + s to make a word plural. It's sure to make a long-deceased grammar nazi turn in his grave.
Say hello to my army of cat's.
Flower's for Sale
These donut's are delicious!