First step to getting voice acting work is make make a demo reel. This will demonstrate your range and what you can do. There are 2 different types of demo reels: Commercial and Character.
Commercial is basic formal reading that you would hear for commercial voice overs (e.g. trailers, product adverts, etc)
A character demo reel is, as you can guess, characters. Play different characters and display you acting skill.
You can make these specifically for the demo reel and/or you can take from previous work.
If you need help coming up with things to say for these demo reels, go to Reddit and find the forum /r/recordthis
On this reddit, they have written up different copies for people to try there demo reels. There are pretty good
Example: My character demo reel:
Once you have done this, it can greatly help getting voice over jobs.
If you are looking for more voice over opportunities in games, fandubs, cartoons and all sorts. I would suggest visiting the forums: The Voice Acting Alliance and The Voice Acting Club. They are brilliant places to get started in voice acting
I wish you the best of luck and if you have any further questions, please feel free to PM me