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' gym
• countries, countries' agreement
• horses, horses' barn
• students, students' homework

An 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 bike
• country, country's border
• boss, boss's office
• children, children's shoes

An 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