The main difference between Chinese and western eating habits is that unlike the West, where everyone has their own plate of food, in China the dishes are placed on the table and everybody shares. If you are being treated by a Chinese host, be prepared for a ton of food. Chinese are very proud of their culture of cuisine and will do their best to show their hospitality.
And sometimes the Chinese host use their chopsticks to put food in your bowl or plate. This is a sign of politeness. The appropriate thing to do would be to eat the whatever-it-is and say how yummy it is. If you feel uncomfortable with this, you can just say a polite thank you and leave the food there.