Accusative Dative Nominative and Genitive
I've been so confused about where and when to use Acc., Dat., and Nom. cases, but I think I've finally figured things out and maybe it'll help you too.
Think of it like He, Him, and his.
So for the NOMINATIVE case you would say "Der Mann schläft." Using Der. So in English it would translate to "The man sleeps." The NOM. case is used to describe who/what is doing something.
For the ACCUSATIVE case you would say, "Ich sehe den Mann." Using Den instead of Der. The ACC. case describes who/what the verb DIRECTLY affects. So in English it would translate to "I see the man."
For the DATIVE case you would say "Ich gab dem Mann einen Apfel." Using Dem. The DAT. case shows who/what is INDIRECTLY affected by the verb. So in English it would translate to "I gave the man an apple."
For the GENITIVE case you would say "Das Auto des Mannes ist schwarz." Using des instead of der or dem AND adding ES or S to the end of the subject. The GEN case shows possession. So in English you would say "The man's car is black." and not "The man car is black."
To sum thing up NOM. = WHO DID IT ACC. = WHO IS DIRECTLY AFFECTED DAT. = WHO IS INDIRECTLY AFFECTED GEN. = WHO'S IS IT
I would strongly suggest that you look at this website. It has helped me A LOT! http://germanforenglishspeakers.com/nouns/declension-tables/
Accusative: direct object
Dative: indirect object