Lesson the first

Apostrophes aren't used to create pluralizations.

Typically, you create a plural by adding an 's' to the end of the word. No apostrophes necessary.

Apostrophes are used to indicate posession. That which belongs to me; Jen's cats. Notice? No apostrophe on 'cats.'

If I wanted to indicate the ball that belongs to the cat, I would say, "the cat's ball." Posession.

If I wanted to indicate the food dishes that belong to both cats, I would say, "The cats' food dishes." 'Cause I like to use that one to screw with people. You could also say, "The cats's food dishes," but it's unnecessary. Not incorrect, though.