When starting a new business, typically, you would apply for a business license with your state or other local government. This is especially true for food service businesses, where you may also need health department approvals, or if you are operating a physical shop. Requirements vary by state, so be sure to check local business resources to find out more about the requirements for your business.
Additionally, you may need to apply with the US Federal Government for an EIN (Employer ID Number). The IRS offers information on its website to guide you on the application process:
https://www.irs.gov/businesses
Most wholesale vendors require either a business license or a Federal Tax ID proving that you would be purchasing as a commercial entity versus a consumer.
Many new business owners elect to incorporate by establishing their business as an LLC (limited liability company) or other type of legal business entity. Be sure to investigate these options (also explained on the IRS website) and the reasons for each as you set up your business.