How does it work with the casus ("Fälle")?

There are four different casus (Fälle) which apply to a noun in German. There is Nominativ, Akkusativ, Genitiv and Dativ. Every casus has a different role.

For example: You would use the Nominativ if the noun you are talking about does something. The question you ask yourself is: Wer tut etwas? "The dog runs." = "DER Hund rennt." However, you would use the Akkusativ if you would talk about that you see the dog. Here, the question you ask yourself is: Wen sehe ich? "I see the dog" = "Ich sehe DEN Hund" Furthermore, you would the Genitiv if you talk about something which belongs to the dog. Here, the question is: Wessen Ball ist das? "That it the dog's ball." = "Das ist der Ball DES Hundes." Similar to that is the Dativ. You would ask: Wem gehört der Ball? "To whom does the ball belong?." = "Der Ball gehört DEM Hund."

As you can see "der Hund" is a more easy noun as it does not change its ending beside when using the Genitiv. Anyway, let's repeat the casus step by step with different examples... Maybe you can create some examples for me?