How do "da-" and "wo-" compounds work with prepositions?
da-compounds (dafür, damit, davon): Used to refer to inanimate objects or abstract concepts that were previously mentioned, avoiding repetition of "Präposition + es/das."
wo-compounds (wofür, womit, wovon): Used to ask questions about inanimate objects or abstract concepts.
Rule If the preposition starts with a vowel, an "r" is inserted (darüber, worüber).
Example
Ich denke an den Urlaub. → Ich denke daran. (I'm thinking about it.)
Ich warte auf den Bus. → Ich warte darauf. (I'm waiting for it.)
Worauf wartest du? (What are you waiting for?)
Wofür interessierst du dich? (What are you interested in?)