is there any requirements i need to present or gave to the immigration of the airport in China?

if i have a valid visa and i went to the airpot is there any requirements that i need to present or gave to the immigration of the airport? what are those requirements?

note:
because i have a friend they missed their flight because the embassy of the airport asking of some document on them but they didnt gave that requirements because no one tell them that they need to present some documents before they can take a flight.and that was their first time to travel in china
hope you can help me to gave the requirements thanks