Talk to someone who is on your town baseball board of directors. Find out who the Chief of Umpires is for that league. Get in touch with that person and find out what Umpire board he belongs to. Most boards are looking for new recruits and will hold training classes over the winter.
You take your exam in the spring, pay your membership dues, register with the assignor and you are working games. You may not get many to start with, but the more you get, the better you get. The better you get, the more you get.
If you have flexibility in your primary job, you can make some good money 7 or more months out of the year. Most of the games pay between 65 and 120 per umpire per game for players in the 13-19 year old range.
It’s not easy. If you have a situation that comes up and it goes awry, you can ask a fellow umpire for help. If you don’t need your answer in a hurry, I can probably point you in the right direction on rules and interpretation.