... in the main text you'll come across the letters N, G, D and A. They are shorthand for the 4 German cases:

• Nominative (N),
• Genitive (G),
• Dative (D)
• and Accusative (A).

The set of 4 different cases is a declension.

In most present European languages the noun shape usually varies to differentiate singular from plural ("hat" / "hats") or feminine from masculine ("hostess" / "host").

In German (and Greek, Latin) nouns also vary according to their logical role within the clause: subject, object or complement.

In English a remnant of this feature lingers in some words: "I" (when a subject in the clause: I saw ...) turns into "me" (when an object or complement: they hit me, they gave it to me, ... received it from me).

Pronoun "who" (as a subject) turns into "whose" and "whom" (the latter for objects and most complements, "whose" for the complement of belonging).

Although cases don't show in all words, a large number of German words do change at least in two or more cases.

QUESTION: What if I don't pay attention to cases and just use the base word?

ANSWER: People might figure out what you mean, but the crudeness of your language racks them.

• NOMINATIVE signals that the word performs as subject (My sister bought a car);
• GENITIVE signals a complement of belonging [of somebody, of something];
• DATIVE signals a complement of destination [to somebody, to something];
• ACCUSATIVE signals an object (My sister bought a car).
  Most prepositions (for, since, over, about etc.) will have the word which follows in dative or accusative; a few in genitive. As to nominative, it is restricted to subjects only.
How it works in practice

In English you write "To Mr. Jones" or "For Mr. Jones" on an envelope. In German, you just write "Herrn Jones".
"Herr" means Mr. and "Herrn" is its DATIVE form, it implies "to Mr. ...", "for Mr. ...".

There are no general patterns for nouns and the dictionary is the only tool available to learn in which cases a particular noun modifies its shape.

Dictionary entries look like the following:

1. Apfel, der; -s, Äpfel

   "Apfel" is German for "apple". First we see the basic word (i.e. its nominative: Apfel). Then an article is shown ("der" is the masculine article and the dictionary adds it to mean that "apple" is a masculine noun). Then "-s" follows to inform that an "s" must be attached when Apfel is in genitive case: "the colour of the apple is ..." »» "Die Farbe des Apfels ist ...".

   Finally, there is the plural form: apples = Äpfel

2. The German for "work" is
   Arbeit, die; -, -en

   The noun is feminine ("die" is the feminine article - like "la" in French or Italian).

   "Arbeit" does not change in genitive singular: "-" means "no change".

   Its plural form is "Arbeiten" (works: just attach "-en" to the base word Arbeit).