I did my own research on a product that I can't find anywhere in the Internet. Do I need to file for both design and utility at the same time? Do I file for a patent over seas meaning China at same time? Please explain, Thanks.
Short Answer: Not necessarily.
These conversations are best had with an attorney, but the answer provided gives you a little bit of background. As always there is a ton more consideration that goes into figuring out whether you want to file for a utility and/or design patent. I can only speak to US patent law, but generally speaking a design patent:
So, it depends on what your product is. If it is a new and useful process, machine, article of manufacture, compositions of matter, or any new useful improvement thereof, you probably want to file a utility patent. If you are trying to protect the ornamental nature of that product you would want to file a design patent as well.
I recommend further reading: What is the difference between a utility patent and a design patent?, and Design Patent Application Guide.
With respect to filing overseas you have a couple of different options, but you will likely be taking advantage of something called the Patent Cooperation Treaty. For more information on the PCT check out this short FAQ from the World Intellectual Property Organization: PCT FAQs.