when I arrive in shanghai pudong airport, will I get bus to Yiwu?

Yes, the transportation is convenient. You can take direct long-distance bus.
After landing at the airport, it's easy for you to find the ticket counter according to the English signs and the boarding sites won't be far from the counters. Don't worry.
The bus schedules are 8:50, 11:30, 14:10 and 17:10. It takes around 4.5 hours on the way.