Plural nouns ending in s add the apostrophe only; ending in other letters they add the apostrophe and s like singular nouns, the Jones' house, the children's toys.
The possessive pronouns never take the apostrophe. We say hers, theirs, its. It's is an abbreviation for it is.
Care should be taken in forming the possessives of phrases containing nouns in apposition, or similar compound phrases. We should say "I called at Brown the printer's" or "since William the Conqueror's time."
An adjective is a word used to qualify, limit, or define a noun, or a word or phrase which has the value of a noun. Nouns are ordinarily very general and indefinite in meaning, for example, man conveys only a very general idea. To make that idea definite we need the help of one or more descriptive words such as black, tall, stout, good.
I saw a man.
gives no definite idea of the person seen.
I saw a tall, thin, dark, old man.
presents a very definite picture. It will be noted that these descriptive words have a way of forming combinations among themselves. It must be remembered, however, that all the words thus used describe the noun. Adjectives are sometimes used as substitutes for nouns. This is one of the many verbal short cuts in which the English language abounds.
The good die young