genitive

dative

accusative

prepositional

Nouns, adjectives, pronouns, and demonstratives do not exist in a vacuum. They serve functions within phrases and clauses. Function determines the case of a noun or adjective. These are five cases listed on this page. More cases exist in many languages. In inflected languages, the forms of pronouns and demonstratives indicate their function. 

In English, function is usually indicated by word order.

Out of his bag, Robert handed Ms. Richards an apple from his family's tree.

subject

function: a noun phrase that performs or experiences the action of a clause

Robert

genitive

function: a noun phrase or pronoun that indicates possession

his family's tree

dative

function: a noun phrase that serves as the indirect object

Ms. Richards

accusative

function: a noun phrase that serves as the object of a verb in a clause 

an apple

prepositional

function: a noun phrase in a prepositional phrase, or the object of a preposition

out of his bag