How do I know which case to use?

There are 4 cases in German- Nominative, Accusative, Dative and Genitive. First you must know the gender of the noun to work out the case. Nominative is used for a person or thing which does the action of the verb. Always used after sein and werden. Accusative is used for a person or thing which is directly affected by the actions of the verb. Dative is used to show indirect objects of a verb, which is usually someone or something which receives the result of the actions of the verb. Genitive is used to show possession. Accusative, Dative and Genitive can be triggered by certain verbs or prepositions.