score:4
Looking on bahn.de for this trip, it seems you take a bus from Frankfurt Airport to Darmstadt.
It says "normal (international) tickets not valid , Subject to supplement", so (I am not sure but) it looks like you might need to pay for that separately.
You say you ordered paper tickets, so if you have not received them yet, it might become clearer upon reading them.
The bus is called AirLiner Direkt and starts here:
Frankfurt airport: Terminal 1 (Bus stop 14), Gate 3 und Terminal 2
You can find the timetable and prices PDF (in German and English) here. A single one-way trip for an adult costs 8.60 Euros and can be payed in the bus in cash or at a machine, where you can pay with Maestro (and maybe credit card).