Honestly, I think the best way to start would just be to record yourself with intent. Find a decent microphone, a quiet room (one with a lot of carpets and blankets, bedrooms are usually good) and some audio editing software, and go nuts. Listen to yourself on the playback, apply some dynamics and EQ to hear the difference between raw and post, and cut together a demo reel if you so desire.

Again I'm not a professional, and I use my voice acting as a component of my job rather than the job itself, but there are agencies just like for traditional actors that'll get your name out there. A website with a portfolio helps. (I wish I had more answers for you, but I really don't know :/)

My first professional voice work was adjacent to my marketing content creation job, I did voiceover for an internal sizzle reel for some kids' toy line (funnily enough, doing my best Wayne June/Darkest Dungeon impression), so I kinda fell into it.

Damn dude... this guy was literally my inspiration for getting into voice acting. I'm not a professional by any means, but if I had never played DD and heard him doing his thing, it would have never even occurred to me to start using my own voice for VO or cartoons.

JD: "Actually, wait, give the list to us first and then we'll release it. I just wanna check something real quick."

"Great shit, kid! That was one in a million!"

What are you talking bro? If woman big strong, means she not small and weak and need big strong man (me) to protect her from all dangers and get validation for my increasingly fragile sense of self worth put in place by generations of archaic social conditioning.