2 answers
Matt’s Answer
Hi there. I would recommend first that you start refereeing at the local level. I started at a local basketball summer camp, then working the local college/university summer camps as a referee, which turned into paid refereeing at the YMCA and then just trying to attend as many high school games and college games as possible and making time to introduce yourself to referees. I sit in games now and there's always one person there monitoring the performance of the referees. Last year, I met an NBA official development scout, attending a game at St. Johns College High School. He gave me his card and said to pass along any talented, young referees who would be good to watch. Try starting with someone you know who may know a referee, or start volunteering at summer/winter leagues to get some practice, exposure, etc. After that, if you're good, people will notice and you just have to ask for feedback, opportunities and how to get connected to the right league, games, etc.
Austin’s Answer
Once you start getting some experience working some small sports games and have met an officiating organization, you can then build enough credibility to start working some travel ball tournaments. While doing this, network and try to meet as many officials as you can so that you can start building a giant pool of officials that you can go to for advice and eventually recommendations. After some time (can be months or years) you can then start getting into high school and then to college. To become an NBA official, it takes some time but certainly isn't impossible, just have to be patient in working in a lot of levels for a few years and making connections with officials in every level you work at.