How to become a voice-actor?
Voice actors are actors - so just like any other actor you would need to get quality training and experience then research and learn the business end of the industry. Actors (even voice actors) are not just "discovered" - it's show BUSINESS and people are in it to make money, not make your dreams come true. Start with basic acting classes and vocal training. You'll want quality classes and a respected coach. Improv classes can be helpful as well as scene study. You'll want to learn how to use your voice effectively and practice, practice, practice. You'll want to work on things like timing, relaxation, projecting a naturalistic tone, microphone technique, releasing inhibitions, and the like. Depending on how you want to pursue your career you may want to learn about recording equipment and set up your own studio and create your demo tapes. Like "regular" acting, there are not a bunch of open auditions you can go to. For most professional work you'll have to be invited to audition, usually through an agent. And you can't just hire an agent. (NEVER pay an agent up front.) Legitimate agents are paid a percentage of what an actor makes, so they're very picky about who they take on as clients. They're looking for trained and experienced actors who have demonstrated they can work at a professional level. Most voice actors are "regular" actors with agents who also submit them for voice work. Networking is the best way to get an agent. If your work with a respected instructor for classes they may be willing to refer you to an agent. And you'll have to learn the business end of the industry. It's NOT that you get an agent and they take are of everything. You need to be in charge of your own career. You'll have to understand the casting process (agents, breakdowns, casting directors), legal issues (contracts, unions, taxes), marketing (resume, demo reel, website, social meal), networking. You'll have to understand the voice industry in particular so like the various genres of voice acting (such as promos, audiobooks, character animation, and automated dialogue replacement), who are the voice over casting directors, what are the upcoming projects. Just like any other actor you'll be starting and running a business where you are the product to be marketed and sold. There's no special steps to go through or boxes to check off and then "viola!" you're a voice actor. It'll be up to you to learn the skills and the industry, understand how you fit in, and run your career. Good luck.
Get into a really good acting school and start learning. Take singing lessons. Join a good community theatre and get loads of stage experience. Actors are actors. Almost all voice work goes to established, very talented, trained, experienced actors. They do voice work in between stage/TV and movie acting to earn extra money.