Akkusativ: den, die, das

The accusative is the case of the direct object: the person or thing the action is done to. Ich sehe den Hund means "I see the dog". Verbs like sehen, kaufen, besuchen, kennen, brauchen, suchen, lesen and haben take an accusative object.

Only the masculine article changes:

• masculine: der becomes den (Ich kaufe den Rock.)
• feminine: die stays die (Wir besuchen die Oma.)
• neuter: das stays das (Ich lese das Buch.)
• plural: die stays die (Ich besuche die Großeltern.)

Watch out: the subject stays in the nominative, even when it comes after the verb. In Wo ist der Bahnhof? or Heute ist der Supermarkt geschlossen, the station and the supermarket are subjects, so the article is der, not den. Ask who or what does the action, or who or what something is. That noun is the subject.