Every sentence in this lesson puts the noun in the dative case — after a dative preposition (mit, aus, seit, von, zu, bei, nach — "with/from/since/of/to/at/after"), or as the person being helped, thanked, believed, answered, etc. (helfen, danken, folgen, gehören, glauben, gratulieren, antworten, zuhören, schmecken, passen, begegnen all take a dative object). The definite article changes depending on the noun's gender:

Masculine and neuter share the same dative article, dem — only the feminine article changes, from die to der. This is the same pattern as the indefinite article, where masculine and neuter shared einem and only the feminine changed (to einer).