during despite because of

Fritz does nothing preposition definite article indefinite article   Fritz macht nichts während des Besuches eines Besuches     trotz der Besuche einiger Besuche     wegen der Feier einer Feier       der Feiern einiger Feiern       des Abendessens eines Abendessens       der Abendessen einiger Abendessen

As you can see, the object that follows the preposition has to be declined according to the Genitive-declination. More details on prepositions you'll find in chapter 19 - more prepositions.

Fritz macht nichts während des Regens. = Fritz does nothing during the rain. Fritz macht nichts wegen des Kindes. = Fritz does nothing because of the child. Fritz macht nichts trotz des Abendessens. = Fritz does nothing despite the dinner. Fritz macht nichts während einer Feier. = Fritz does nothing during a party. Fritz macht nichts trotz des Regens. = Fritz does nothing despite the rain. Während des Abendessens sprechen sie nicht viel. = During the dinner they don't talk much. Während des Spazierganges lachen sie viel. = During the promenade they laugh a lot.

With most of the prepositions the Genitive is only used if there is an inflected pronoun (except for personal pronouns!), an adjective or an article between preposition and noun. Otherwise the Dative is used. This is especially noticeable when personal pronoun e.g.:

Fritz macht alles wegen seines Sohnes (Gentitiv). = Fritz does everything because of his son.
Fritz macht alles wegen ihm (Dative). = Because of him Fritz does everything.

Wir gehen nach Hause nur wegen einer Person (Genitive). = We go home only because of one person.
Wir gehen nach Hause nur wegen Dir. = We go home only because of you.

These few examples just show the principle. All the prepositions that require the Genitive work the same