Apostrophe S (-'s) and S apostrophe (-s') are usually used to form a possessive noun or pronoun. However, they have some differences. Apostrophe s can be used with both nouns and pronouns to depict a singular possessive statement. On the other hand, s apostrophe is used in sentences to depict possessive nouns or pronouns in plural form.
Taking these sentences as examples, sentence one: "The boy's dancing steps were really nice," sentence two: "the boys' dancing steps were really nice." "Boy" in the two sentences is a possessive noun, but note that the first one is "boys," and the second one is "boys'."
This simply means that the first is referring to just one boy, while the second is referring to two or more boys. Moreover, this only works right for regular plurals. When it comes to the case of irregular plurals, for example, children, men, teeth, feet, etc., the case is different. Their possessive forms take apostrophe s and not s apostrophe.