Hello, you have to learn the verbs with their prepositions. In english you say: wait for, in german warten auf You can't just translate it from english. You really have to learn all the prepostions and their case for every verb (which has a preposition) Ich kaufe ein Geschenk für its not a verb with prepostion. the für belongs to the friend. But warten always comes with auf. More verbs: fragen nach, freuen auf, sprechen mit/über, leiden an, bestehen aus... there are many many many more..search for "Präpostionalverben" or "Verben mit Prepositionalergänzung", you'll find them all! Happy memorising! :)