Do I need to do anything before my flight if I stay in Beijing for 4 hours or for 6 and a half hours

I will fly from Munich to Seoul and back, both times changing flights in Beijing, where I have to wait for 4 hours on the way to Seoul and for 6 and a half hours on the way back.
Do I need to do anything before my flight to be able to stay in Beijing or will I just have to fill in the form that they hand to every passenger during the flight?
I don't need to apply for a visa for South Korea, because I'm from Germany and I can stay there for up to 90 days without entry permit.
If I arrive in the airport of Beijing without any special documents, will I have any trouble? I don't plan to leave the airport, I'll just wait there for my next flight.