This can be solved by doing a quick search on the Internet or by talking to all your connections at your boxing club. When you're ready, your coach will likely let you know. You'll likely know, too. This step is more paperwork than anything. Visit USAboxing.org (if you're based in the US, of course) to get a list of information by state. Once you do this, you'll be able to find open events that you can participate in. You will do this by filling out an application and undergoing a physical examination from your doctor. This is done at the state level through the State Athletic Commission when it comes to the US. You will have to contact the necessary people to get your license to compete in events. There is a minimal fee and it varies by state. Other than that, it's just a bunch of forms and a physical assessment. These events are the way most fighters get their initial experience. The fights don't count towards your record, but are the safest and most practical way of getting experience. You'll be able to find them through connections and through your organization's website, which should post upcoming events. You'll be classed by age, weight, and record initially. You can be an amateur boxer in the US at just 8 years old! The difference between amateur and pro boxing is that you will be allowed to wear protective headgear. This is essential in the beginning stages of your fighting career in order to prevent potentially fatal injuries while you learn to protect yourself.  Again, you will be placed according to your weight, age group and class, which will begin as "novice" if you're 17 or older. You'll start out in local and regional tournaments, with a long-term goal of competing in the U.S. Amateur Championships and earning a spot on the U.S. Boxing team. Some coaches are pretty sketchy. They'll encourage to fill a slot in a weight class just so you can get going and they can start profiting off of you. Don't do this – sometimes it's just not healthy and your body will take to injury much more easily. Only...

TL;DR in Vietnamese:
Tìm tổ chức quyền anh nghiệp dư tại địa phương. Đăng kí như một vận động viên nghiệp dư. Tham dự những giải đấu quyền anh không được công nhận. Bắt đầu với vai trò một võ sĩ nghiệp dư. Đừng vội đăng kí vào chỗ trống trong hạng cân. Làm cho cơ thể săn chắc hơn.