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.
Dieter's dog brings him the newspaper.
Hans' Hund ist zu alt dafur.
Hans's dog is too old for that.

OK, full disclosure: an increasing number of Germans use the English-style apostrophe (“Dieter’s Hund”) and in the ’90s it was even approved as an alternative form by Duden, the German dictionary publisher. But to say that some Germans disagree with this “reform” is putting it mildly. Play it safe and leave the apostrophe out. And this has nothing to do with the erroneous use of the apostrophe with a plural s (“the dog’s are barking”) which is just as incorrect in German as it is in English.

Certain prepositions can make it hard to identify cases. For example, in “the deer ran through the forest,” is the forest a direct or indirect object? Fortunately it doesn’t matter, because every ambiguous preposition in German is associated with a specific case for the following noun. You’ll learn these when we cover prepositions in Section VI.