If you are not a citizen or a lawful permanent resident, you may need to apply for an Employment Authorization Document (EAD) in order to work in the United States.
The specific categories of foreign nationals that require an EAD include (but are not limited to) asylum seekers, refugees, students seeking particular types of employment, applicants seeking to adjust to permanent residence status, people in or applying for temporary protected status, fiancés of American citizens, and dependents of foreign government officials.
If you are authorized to work for a specific employer, such as a foreign government, you do not need an Employment Authorization Document.
Once you get your EAD, you will then also need to get a business permit from your local city or county where you set up shop. If you will have employees, you will need to get workers’ compensation insurance, and will need an understanding of tax withholding laws.