رضا: In English, there is only one case. All the nouns are written and pronounced in the same way no matter where it is in a sentence or what kind of preposition precedes it. However, in a lot of languages, nouns do change (or their articles). In Czech, each noun (and also adjective, pronoun and numeral) has seven forms. Anybody who studies Czech as a foreign language should learn all these forms and remember which suffix goes with which case. For instance if you want to say "by bus", you should know that this is a 7th case and the suffix is -em ("autobusem"). Accordingly, "without anything" is a 2nd case and the suffix is -ho ("bez ničeho"). I hope it makes some sense. :)