Go to the USSSA website representing the region where you live and let them know that you want to umpire baseball games. Fill out an online form and the USSSA will contact you to confirm your interest. If you have umpired for other organizations, you may be given assignments right away. If you have not umpired previously, you will be asked to take a course.
Take a course on the rules of baseball and how to enforce them as an umpire. You will be given specifications on how to call balls and strikes, where to stand on the base paths and how to handle disputes. You will also be given a rule book and a case book that allows you to see how plays were called in games.
Take a test to make sure you know the rules of the game. The test presents the rules on a case-by-case basis and you have to choose the correct way of deciding the play. The test is designed to make sure each umpire has some knowledge of the way the game should be adjudicated.
Start taking assignments to umpire games. If there are no problems, you will be put on the regular roster and given assignments throughout the baseball season. However, if managers and coaches have questions about your ability to call balls and strikes correctly, you may have to meet with administrators before your get new assignments.