Every sentence in this lesson puts the noun in the accusative case — the direct object of a simple everyday verb (haben, sehen, brauchen, kaufen, essen, trinken, and similar). The definite article changes depending on the noun's gender:

Feminine, neuter, and plural keep the same form they have in the nominative — only the masculine article changes, from der to den. This is the same pattern as the indefinite article, where only the masculine form changed between nominative and accusative (ein → einen).