There are a few ways you can go about discovering an Industry NAICS code.
The easiest way to do so is to visit the Census' NAICS page. You can then either do a keyword search for your industry on the left hand side of the screen, or you can browse the Classification system by clicking on the reference files (also on the left).
Please be aware that newer industries may not have a NAICS code. Social Networking sites, for example, were only recently added to the 2017 NAICS, and were not previously a recognized industry.
62 = Health Care and Social Assistance
6211 = Offices of Physicians
621111 = Offices of Physicians (except Mental Health Specialist)
621112 = Offices of Physicians, Mental Health Specialists
These codes help you to identify competitors, and they can help you find resources that will tell you more about your company's industry.
These codes are used throughout many of the databases that you will be using for this assignment.