There are four “cases” in German, which correspond to four different roles a noun can play in a sentence. The first three are fairly straightforward: the nominative case refers to the subject of a sentence, the accusative case refers to the direct object, and the dative case refers to the indirect object.
Der Schüler gab dem Lehrer seinen Bericht
The student gave the teacher his report.
NOM DAT ACC
The final case is the genitive, which expresses possession or belonging and corresponds to the English ‘s. It looks a little different in German than in English, with the possessor and possessed in the reverse order:
Der Hund meines Bruders bringt ihm die Zeitung.
NOM GEN DAT ACC
My brother’s dog brings him the newspaper.
GEN NOM DAT ACC
You can use the English-style genitive “s” in German, but only with names – and without the apostrophe.
Unless a name ends in “s,” in which case you use the apostrophe without the additional s. (In English we do that with plural nouns, but that doesn’t come up in German since this form of the genitive is only for names).
Dieters Hund bringt ihm die Zeitung. | Hans' Hund ist zu alt dafur. |
Younger people, mainly when speaking – avoid the genitive case by using the preposition von, which is like avoiding it in English by using of:
my brother's dog | --> | the dog of my brother |
der Hund meines Bruders | --> | der Hund von meinem Bruder |
they’re both perfectly correct.
What’s not correct is to use the dative case instead of the genitive without the von.
Der Hund meinem Bruder would be just as wrong as the dog my brother.