>>>I always thought that a language that had 500 Irregular verbs had a problem.<<<
Try to memorize the articles and endings in German. LOL
So, dog = "pies" in Polish and bottle = "butelka", but if I want to say
This is a good dog, this is a good bottle, I say "To jest dobry pies, to jest dobra butelka"
But, if I want to say "In the room is a good dog and good bottle", I say "W pokóju jest dobrego psa i dobrą butelkę" --> Accusative, pies becomes psa and butelka becomes butelkę
Now, if I want to say "I have a good dog. I have a good bottle" it is "Mam dobrego psa i dobrej butelki" --> Genitive pies becomes psa and butelka becomes butelki
then "I think of a good dog and good bottle" is "Myślę o dobrym psie i dobrej butelce" --> Locative, pies becomes psie, butelka becomes butelce
Then "Thanks to the good dog and good bottle" is "Dzięki dobremu psowi i dobrej butelce" -> Dativa
"I am with the good dog and good bottle" = "Jestem z dobrym psem i dobrą butelką" -> Instrumental
Vocative is only used for expressions of "To Mr. ...." etc.