Grammatical case are things in a language that shows what role the word has in the sentence.
The nominative case shows that the noun is doing the action; the accusative case shows that the action is done to the noun; the locative case shows that the action is done on or at the noun, etc etc, there are many more (but no language has them all).
Case endings are suffixes attatched to nouns which denote the case of the noun.
