No one has trouble making a dog possessive: the dog’s collar. Even more than one dog isn’t confusing: the dogs’ collars. But a few situations make people scratch their heads:
What if the possessive word ends in a vowel? How do you make the name Garcia possessive? Just add ‘s to whatever the owner word is: José Garcia’s house.
What if the owner word ends in an S, such as Garcias? Again, whatever the owner word is, add ‘s: the Garcias’ house. However, when you add that ‘s and the new possessive word ends in two or three esses, the preference today is definitely to remove that extra S: the bus’ doors, my boss’ desk.
What if the possessive word ends in Z? Again, add ‘s: Julia Martinez’s office.
Here is the apostrophe rule distilled for you:
No matter what the word is you want to make possessive, take that owner word and add an apostrophe and an S. Then, if the new word now ends in two or three esses, drop the S after the apostrophe. It’s that simple.
One caveat: Don’t reach deep into your apostrophe pocket and throw one in where it isn’t needed. Ask yourself if the word is just a plural: The Garcias are moving. Eggplants are on sale. Sarah has two bosses.