Several languages make use of so-called cases.
In English cases are not used and therefore most people won't know what cases are. But in many other languages, such as German and Russian there are cases. Unfortunately cases make a language a lot more difficult to learn. A case certain 'mode' a word appears in, nouns, pronouns, articles and adjectives usually get a special ending depening on in what case they are. Cases appear at a certain place in the sentence or after certain prepositions.