Normally, people have found the factory, or factories, they are interested in before they arrive. Sometimes you will have decided which ones are your main candidates. In any event, I am occassionally asked if I can find or know of one that will makes product X or Y. There are thousands of factories in the Shenzhen area, perhaps ten's of thousands. It is usually best if you find possible sources in advance of coming here. When we actually begin going out and seeing with our own eyes and meeting people is when you can make concrete decisions. If you are going to be visiting lots of them, it's often useful to rent a car with a driver. I have a separate page regarding that here.