akussitiv, nominativ, dativ og genetiv: Hvad er det?

You can inflect a noun into different cases.

The case depends on the function of a word.

Nominativ (-> to nominate) is for the subject of a sentence, that what is acting. In languages like English or Danish, it is in the beginning of a sentence (if not time/space goes first^^) (Der Mann trifft seine Freunde.) - The man meets his friends. <- the man does something so he's to be Nominativ

Akkusative (-> to accuse) something is done to someone/something. The normal object form. Der Mann trifft seine Freunde. - The man meets his friends. <- the friends are met, so they are object.

Dativ - used for several verbs instead of Akkusativ, such as helfen. Der Mann hilft seinen Freunden. <- helfen demands Dativ

Also indirect object: Der Mann gibt seinen Freunden gutes Bier. <- seine Freunde = Dativ, they get something ; gutes Bier= Akkusativ, the beer is given.

Genitiv is the case of possession: Die Freunde des Mannes. - The man's friends.   Das Bier der Freunde -  The friend's beer.

(basically just like Genitiv in Danish)

If you use Dativ or Akkusative depends on the verb.

In prepositional expressions they can also depend on the preposition.

Anstelle des Biers hatte der Mann Cola zur Party mitgebracht. - instead of the beer, the man brought Cola to the party.

- anstelle demands Genitiv, so that's what beer has to be.

- zu demands Dativ -> zu der Party (dativ)

Ìt just depends on the prepositions.

http://www.canoo.net/services/OnlineGrammar/Wort/Praeposition/Kasus/index.html?MenuId=Word73

That's a lot of information already I think, have fun.

Bedste hilsner

kan jeg få det på dansk? xD

But if you can't write in danish, then it is okay :)

Mit dansk er meget dårligt. :P

Jeg kan skrive lidt og forstår det meste, men jeg kan ikke forklare det på dansk, undskyld. :)

But feel free to ask if you didn't understand any part of it, so I can try to clarify it. :)

Have a nice day!

No, mate that is not necessary. 
Thank you for your help.

you're welcome :)