It depends on what kind of travel agent you want to be.
If you want to work for a salary in a storefront travel agency, then the traditional career path is to enroll in a travel school and be trained to operate one of the GDS systems that travel agencies use to make bookings. Then you will start at a low entry-level salary and, hopefully, work your way up.
If you are the more entrepreneurial type and want to be your own boss, there are two ways to be come an independent travel agent these days.
1.) Form a business relationship with an existing travel agency. You would be an independent contractor with your own clients, but you would pass your bookings through the travel agency, using their industry identifier to reassure the supplier that they are dealing with a "real" travel agent.
Then you and the agency share the commission according to a negotiated split, which can range from 50% to 80% to you.
There are many travel agencies that will work with newcomers on this basis. Most, but not all, require a fee to affiliate with them.
2.) Get your own industry identifier and deal directly with suppliers. This is easier than it may sound and it can actually cost less than the fees charged by some of the agencies mentioned in #1.
I don 't recommend this second strategy to newcomers, however. Wait until you have some experience before you decided whether or not it makes sense to strike out on your own.