What are apotrophes?

When do you add an apotrophes at end of word?

An apostrophe is added to the end of a noun for the possessive form of a plural noun ending in -s. Examples:boys, boys' gymcountries, countries' agreementhorses, horses' barnstudents, students' homeworkAn apostrophe plus an -s is added to singular nouns and plural nouns that don't end in -s for the possessive form. Examples:boy, boy's bikecountry, country's borderboss, boss's officechildren, children's shoesAn apostrophe is added to the end of a word when the last letter or letters have been dropped in informal speech. Example:"Wishin' and hopin' and thinkin' and prayin', plannin' and dreamin' each night of his charms, that won't get you into his arms..." Hal David and Burt Bacharach