I haven’t been a travel agent (TA) myself, but I worked for a company that was part travel agency, and they did lots Disney (AAA Travel, specifically the one with Auto Club of Southern California). I don’t know all the details, but here are a few things:
BIG DISCLAIMER: I haven’t worked at a travel agency in 5ish years and this is a mix of memory and Google-Fu.
The official Disney TA site is https://www.disneytravelagents.com/
You need to have an IATA/IATAN or CLIA number to do much with Disney’s TA stuff. Both are Travel Agency ID numbers. IATA is required to issue airline tickets. CLIA is from the cruise line industry and doesn’t allow issuing airline tickets. You generally need to have some form of business to get either number, you can’t just sign up and not do anything. I am not sure about CLIA but IATA requires proof you are making travel sales before they accredit you.
Several sources I read state very firmly that you only get to do Disney TA training (like the College of Disney Knowledge courses) after you are already a travel agent. It’s not a program to get you into the business.
My personal advice is to find an existing travel agency to hire you. From what I have seen, Disney-specific agencies often want people with existing Travel Agent experience, so you may have more luck looking for Agencies that do all kinds of travel. Often, you start out doing walk-in stuff at a physical agency or other work to try and drive new business, and over time (years) you build up your own client base. If you leave, sometimes part of that base will follow you to your new agency. But that takes a lot of time and work.
This specific post on wdwmagic, while old, has some good general info about what to expect http://forums.wdwmagic.com/threads/how-to-become-a-disney-travel-agent.859450/#post-5308210