What's the difference between the accusative and the dative case and when should I use them?

The accusative and dative are two of the four cases that are used in the German language. The accusative case is used to mark the direct object of a sentence (bold in the example below):The man eats the apple .Der Mann ißt den Apfel.The dative case is used to mark the indirect object of the sentence (bold in the examples below):The man gives the apple to his friend. / The man gives his friend the apple.Der Mann gibt den Apfel seinem Freund. / Der Mann gibt seinem Freund den Apfel.The dative is used in this sense to mark the action of giving the apple to his friend, rather than the man giving his friend to the apple. Geben is one example of a verb that requires the use of the dative case, but there are many others, including antworten, gefallen and helfen. The accusative and dative cases are also used in conjunction with different prepositions. When any of these prepositions are used, the noun following immediately afterwards will take the respective case.Accusative case prepositions: für, um, durch, gegen, entlang, bis, ohne, wider.E.g Ich habe ein Geschenk für dich.Dative case prepositions:aus, außer, bei, mit, nach, seit, von, zu.E.g Ich wohne bei meiner Mutter.However, there are also a set of prepositions which are known as 'dual case' prepositions. These prepositions are: an, auf, hinter, in, neben, über, unter, vor, zwischen.They are called dual case prepositions because they can take either the accusative or the dative case depending on the situation in which they are used: the accusative case is used when referring to direction or motion and the dative case is used when referring to location.E.g Die Kinder gehen in die Schule. (Accusative case because 'in' refers to the movement of the children).E.g Was habt ihr heute in der Schule gelernt? (Dative case because 'in' refers to what was learnt in the location of the school)