What is the point of cases in German? What is the difference between them?

German uses cases to convey information about the grammatical roles words play in a sentence. In English, this information is often conveyed using word order. The fact that German uses cases instead means that German word order is much more flexible than English word order. We do have some examples of case marking in English. For example, you would say 'She hit him, so he hit her back'. In this example, 'she' and 'he' are the subjects of the sentence and are therefore in the nominative case. 'Him' and 'her' are the objects of the sentence and are therefore in the accusative case. You can't say 'him hit she', because the rules about English word order don't allow it. In German, however, things are more flexible. For example, in the sentence 'der Hund beisst den Mann', the dog (der Hund) is in the nominative case and the man (den Mann) is in the accusative case, showing who is the subject and who is the object. If you wanted to emphasise that the dog had bitten the man, as opposed to someone or something else, you could rearrange the sentence and say 'den Mann beisst der Hund'. The case markings mean it's still clear who is doing the biting and who is being bitten.