I will be traveling to China with United States passport. What visa do I need and where do I get it

What's the purpose are you going to China? If it is for sightseeing, you can apply for a tourism visa.
You can go to the China embassy or consulates to obtain the visa. Check which consular district you belong to and you should go there to apply for the visa: https://www.travelchinaguide.com/embassy/united_states.htm