sorry, if I bore you, but when I came to Germany nobody explained to me what all this boring stuff like dativ meant. I make it simple:
-Nominativ is only used for the subject:
der Mann, die Frau, das Kind >the man, the woman, the kid.
Bsp: Der Mann arbeitet = the man works
-Akkusativ is only used for "normal" objects:
den Mann, die Frau, das Kind >the man, the woman, the kid.
Bsp: Ich habe den Mann gesehen = I've seen the man
-Dativ is used for to+object:
dem Mann, der Frau, dem Kind > to the man, to the woman, to the kid.
Bsp: Ich gab dem Mann Geld = I gave money to the man
-Genitiv in a sentence is used for of+object:
des Manns, der Frau, des Kindes >of the man, of the woman, of the kid.
Bsp: Die Tugend des Mannes = the virtue of the man