Hello , From Hong Kong Airport, How do i get to Foshan City ?

Assalamu alaykom!
You can go to Guangzhou first and than take the long distance bus to Foshan Chancheng at the Liuhua bus station. I have been there for many times, it takes about one hour to get to the ceramics whole sales market and it costs 43 RMB. If you need any help, please let me know, maybe I can help you.

The city is pretty big. I think the markets you mean are in Shiwan,which is Chancheng District, there are markets of ceramics. You can take a bus or a train.
Buses are convenient enough, just go to any of those hotels in the city and it will be really convenient to take a taxi from those destinations. And here are a bunch of buses or trains you can take:

http://prdguide.com/search?utf8=%E2%9C%93&from=Hong Kong International Airport&to=Foshan&vehicles=all