What are the different cases in German and how do I know which to use?

There are 4 main cases in German, the nominative, accusative, dative, and genitive.

The nominative case is the subject of the sentence: what is doing the action - 'THE MAN throws the ball'

The accusative case is the object of the sentence: what is having the action done to it - 'the man throws THE BALL'

The dative case is the indirect object: what recieves the object in the accusative - 'the man throws the ball to THE DOG'

The genitive case shows possession: who owns the object - 'the DOG's ball' (the ball OF THE DOG)