Das Hemd passt dir nicht. Es ist zu groß.
Many German verbs need an object. The object is often in the accusative case. However, some German verbs are used with a dative object. The dative object is often at the receiving end of an action, and is therefore commonly a person. The verbs passen and stehen are examples of verbs used with a dative object.
Das Hemd passt dem Mann nicht.
Die Hose steht der Frau nicht.
Der Pullover passt dem Kind nicht.
Die dunklen Jacken stehen den Kindern nicht.
We can use a personal pronoun as the dative object; in this case, the personal pronoun has to be in the dative case:
ich -> mir
du -> dir
Das Hemd passt mir nicht.
Der Pullover steht dir nicht.
The dative object answers the questions who? ("Wem?") or what? ("Was?") (wem for people and was for objects).
Grammatical terms in German:der Dativ: In German, there are four different forms or categories (cases) of noun, called Fälle or Kasus in German. As well as nominative and accusative, there is dative. Nouns take this case when they come after certain prepositions, for example, or are the object of a verb that takes the dative case. The articles take the following forms: dem/einem, der/einer, dem/einem, den/-. In the plural, an -n is often added to the end of the noun.