Generally speaking the accusative case is used for the direct object in a Sentence, whereas the dative case is used for the indirect object of a sentence. For example in a Sentence such as 'I give the key to him.' 'the key' is the direct object, and the pronoun 'him' is the indirect object. So in the german translation of this sentence ' Ich gebe ihm den Schlüssel.' the direct object 'den Schlüssel' is in the accusative case [DER Schlüssel (nominative singular) becomes DEN Schlüssel (accusative sing.), the personal pronoun 'ihm' is the dative form of 'er' (just like in english 'he' changes to 'him'). What makes the whole issue a bit more complicated though is that there are certain prepositions that always require the noun they precede to be in the dative case and others that always require the respective noun to be in the accusative case. Furthermore there are so called 'two-way prepositions' that require either the dative or the accusative depending on whether motion towards something (accusative) or static position (dative) is involved. check out the following links for further clarification: http://www.nthuleen.com/teach/grammar/nomakkdatexpl.html https://yesgerman.com/learn-german/lesson-20-dative-und-accusative-prepositions/ http://germanforenglishspeakers.com/prepositions/two-way-prepositions/