In the United States you do not need to register. However, you may need a license depending on your industry and location. For instance, many consumer-facing businesses such as food preparation or pest control require licenses or permits. Check with your municipality, county or state.
In conclusion, there’s a lot to consider to become self-employed. If you are someone frustrated with cubicle life, working for yourself may give you more autonomy. Remember, though, as a business owner you ultimately answer to customers or clients and must satisfy them.
Information Sources
Small Business Statistics
IRS. “Self-Employed Individuals Tax Center”
IRS. “Gig Economy Tax Center”
IRS. “Publication 535”
IRS. “Independent Contractor or Employee”