How do I use the accusative case?

The accusative case is most commonly used when referencing the direct object of a verb, in other words the person/thing that the verb is being done to. For example in the sentence "the boy kicked the ball" the ball would take the accusative case, as it is being kicked. In practical terms this does not change the noun, but does mean that the article (der, die, das) or equivalent must take accusative endings. Conveniently, neuter, female and plural don't change from the nominative das, die and die. It is only masculine 'der' that changes to 'den'. Similarly adjective endings only differ from nominative adjective endings for masculine nouns, ending in 'en' instead of 'e'. Another use of the accusative is after the prepositions: für, um, durch, gegen, bis and ohne.