I am a US resident, but i hav a Nigerian passport. What are requirements for applying 4 Chinese visa

If you visit China for sightseeing purpose, you need to prepare a completed application form, a passport-style photo, passport and its photocopy, round trip air tickets, hotel booking record, and an invitation letter from a duly authorized unit, as well as other materials the consular officers consider necessary.

How can i show air tickets and hotel details when i do not have a visa yet??

You should book the tickets and hotels beforehand, and then provide the transportation and accommodation arrangement to make the application from the China embassy.