You won't make a living from it.
Look for your national amateur commission, and they'll have a process you need to follow to get you started. It usually requires a test, usually practical, then some practice experience. You'll need a fair few years amateur experience before you go up to to professional level, if it ever happens.
For sanctioned fights, you need the experience. Once you have a respectable reffing/judging experience, you can send an application along with references to a professional commission. If accepted, you should join and start paying your dues (membership fees) for a sanctioning body, and they'll give you assignments as well as possible assignments from the commission. In a lot of cases, judges are usually members of a certain sanctioning body (i.e IBF-only refs and judges). From here, you see what is available.
Also, it is not unusual for an sanctioning body to "request" a portion of your pay to go towards their version of a Boxer's pension fund. I know the IBF do this, and I think it's a pretty good idea. You usually get reimbursed for expenses, though it's up to you to pay for everything before that. The pay isn't great.
Takes a LONG time for it to take off. You are much better off starting in Europe than you are in the US. More ways to get into the system (so many different national, local boxing commissions)