The genitive case signals belonging or possession.
It is used in noun-noun constructions, as well as after certain verbs, prepositions, and adjectives.
The question for the genitive case is "Wessen?" (Whose?)
⇒ Wessen Pferd ist weiß? – Des Reiters!
⇒ Noun-Noun Construction ⇒ Genitive
The preposition "während" requires the genitive case ⇒ des Spiels
Masculine and neuter nouns require an extra ending in the genitive case: "-s" or "-es."
Nouns that end in -s, -ß, -x, -z: ("-es" MUST be used)
One-syllable nouns: (Just an "-s" is ok, but "-es" usually sounds better)
For all other nouns: just "-s" (required)
Belonging will normally be shown using a noun-noun construction.
The noun being "owned" is put in whatever case it would normally be in - it goes first in the noun-noun construction.
The "owner" is put in the genitive case - it goes second.
In noun-noun constructions you can avoid using the genitive case by adding the preposition "von" between the nouns and putting the second verb in the dative case.
Because there is no article, we have to signal the genitive in a different way:
The proper noun (the "owner") goes to the front and requires the ending "-s."
If the proper noun ends in s, ß, x, or z, an apostrophe is needed:
The preposition "wegen" can only be followed by the genitive case.
The most important genitive prepositions:
"Während," "wegen," "trotz," "innerhalb," "außerhalb," "oberhalb," "unterhalb," "aufgrund," "anstelle," "(an)statt"
If there is a preposition, the rule of the preposition applies, no matter which case the verb would normally require.
Einer Sache: gedenken, bedürfen, Herr werden
Jemanden einer Sache: anklagen, bezichtigen, überführen, beschuldigen, verdächtigen
Sich einer Sache: brüsten, erinnern, erfreuen, enthalten, schämen
More about verbs with genitive complements.
Also: "überdrüssig," "verdächtig," "würdig," "bedürftig"
The adjective always comes after the noun and stays in its base form.
If you are now thinking "How can I learn all of this stuff? Adjectives, verbs, prepositions, …"
Don’t worry! The genitive case isn’t used very often anymore.
You can often avoid the use of the genitive (and therefore having to know the genitive rules) by using prepositions instead:
We can use the preposition "an" to outsmart the genitive case. The preposition is then followed by the noun in the accusative case. The case always depends on which word (here the preposition) comes before the noun.
You can also avoid the noun-noun constructions by using the preposition "von" to get around it.
But be careful: In noun-noun constructions the genitive is still used, since the sentence sounds better using the genitive case. But both are grammatically correct!