Businesses do not need a license to act as an importer. However, some items require a license or permit from various government agencies in order to be imported. For more complete information, please see the U.S. Customs publication "Importing Into the U.S."
The chapter on "Special Requirements" provides complete information.
U.S. Customs and Border Protection (CBP) paperwork does require an "importer number" as a means of identifying who the final recipient of the goods is. If you have a business tax number with the IRS, this number should be used as the importer number. If you do not have a business tax number, you may use your Social Security number.
A Customs Broker clears goods through CBP on behalf of importers who do not want to handle the various technicalities that are involved in importing.