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!