Cases

Every language has at it's most basic level a set of building blocks that are used to piece together an assembled sentence. Nouns, verbs, adjectives, and prepositions are some of the more familiar blocks that we use constantly in the course of normal conversation. These blocks can be placed into sub-groups within the whole sentence based on whether they refer to the subject or object of the sentence, or some other additional element. In English have to think about where a block appears in a sentence because it directly affects the meaning. German is less sensitive to word order because it makes more extensive use of cases than English. But even in English, if you don't get the cases correct you can end up with nonsense like this:

With German you can't properly use nouns, pronouns, articles, adjectives, prepositions, and many other assorted language elements until you understand the four cases. The next four sections deal with each case in turn, explaining their usage and examples.