What must I do to establish a new business in Nassau County? To file a business name, you need to complete the necessary documents.How to fill out the Nassau County License Application Instructions? 1. Gather all required documents and photographs. 2. These are documents and forms relating to the areas in which they are located. Most documents and forms on this website are in Adobe Acrobat (. After a final review of your license application, you will be sent instructions for the fingerprinting process. You must complete the application process, including signing the last page of the application and being interviewed. Be sure the applicant's name is the same on all documents. See "Instructions for Completing an Application" for more details.