Some verbs used extensively with certain prepositions to convey specific meanings. An example of this is in the verb “to wait”:
I wait for the bus. / Ich warte auf den Bus.
In these sentences, the prepositions “for” and “auf” are required when discussing the act of waiting with a direct object. There are a number of such verb + preposition combinations in German, and they lend themselves well to a shortened way of referring to an entire prepositional phrase. Consider the following continuation of the above example:
I waited a long time for it. / Ich habe lange darauf gewartet.
In English, the substitution of the pronoun “it” for “the bus” is not unlike the German, with one caveat: the preposition is combined with “da” and adds an ‘r’ before the preposition if it begins with a vowel (e.g. an → daran). These “da-compounds” (Präpositionaladverbien) can be used to refer to something already mentioned, however, they cannot be used with people — it would be insulting to refer to someone as “it.” In the case of people, the personal pronoun can be substituted for the person.
I waited for Joseph. I waited for him. / Ich habe auf Joseph gewartet. Ich habe auf ihn gewartet.