Ich warte darauf.
English: I am waiting for it.
Pronominaladverbien are special German words made by combining 'da-' or 'wo-' with a preposition. They replace things (not people) in a sentence, especially after prepositions.
You use Pronominaladverbien when you want to refer back to something already mentioned, especially after a preposition. They are often used with verbs that require prepositions, and in questions or answers about things (not people).
Ich warte darauf.
English: I am waiting for it.
Womit schreibst du?
English: What are you writing with?
Wir sprechen darüber.
English: We are talking about it.
Worauf freust du dich?
English: What are you looking forward to?
Dafür interessiere ich mich.
English: I am interested in that.