If you haven't already, I recommend to start by creating accounts on platforms like Actors Access and Casting Networks (there are others but these two have a lot of activity). Set a phone up with a selfie timer or have some help take a few simple photos full body, profile, 3/4, and decent head shot. You can also start uploading sample videos of your skills or a short introduction that shows your personality.
From there, you can begin self-submitting top whatever rolls and open castings peak your interest, typically there are tons of options that only require a short video submission as long as you fit some of the role criteria.
An agent will certainly open up the door for bigger roles and more legitimate connections, but it helps to get the ball rolling yourself first. If you have any more questions I'd be happy to take a call!
I would take some time to find a good and legit agent, not a big one, specially if you are starting. Sometimes a small/ medium size agency will give you more attention and more experience ( what is exactly what you need to biuld). Be aware of scams while searching for agencies, one good way is asking for a list of clients, models, and actors who have worked with the agency ( if possible contact them and ask for a realistic insight). And if the agency doesn't have a website, that's suspicious. Even if they do, any guarantees they make about modeling jobs or requests to pay up front still make it a scam. And never go alone for these meetings, be safe. Good luck and never gave up!