Single or return?
Buying a ticket is a two-line dialog:
- You: Einmal nach Bonn, bitte.
- Clerk: Einfach oder hin und zurück?
einfach = one-way, hin und zurück = there and back (round trip). Add zweimal for two people.
Tip
einfach also means "easy" — at the ticket counter it always means one-way.