This information is by no means definitive or exhaustive - it's simply based on my personal experiences and what I've seen work successfully for others. These are things that have worked for me in the realm of online voice over specifically and hopefully they can work for you as well.
Before You Start
When it comes to stepping into the world of voice over online, an important thing to realize is that you will not just be an actor who comes into the studio and records what is put in front of you. While you have the flexibility of setting your own hours and working from anywhere in any country, you are also your own agency, engineer, and technician. This will mean you need to know how to find work and create and deliver content all by yourself. Fortunately, this is not as hard as it sounds, but it's not going to be as glamorous as you think and there's not always a lot of time behind the mic.
Crash Course Online Voice Over is not going to be about acting, at least not as it's primary goal. This is not because acting isn't important, but because there is no special acting you do when you are a voice actor online. At the end of the day, you will be an actor, regardless of where or how your acting is utilized. You need to be a good actor to be a good voice actor. You need to be a good actor to voice act in a studio just as you need to be a good actor to voice act online. While acting may be touched on later, there is still a lot of information to cover before focusing on acting technique.
If you are interested in more information on acting, specifically for voice actors and anyone interested in animation and video games, there are already a lot of great resources available that I would highly recommend in getting started:
Talking Toons - Podcast by voice actor Rob Paulsen (Animaniacs, Pinky and the Brain, Jimmy Neutron
Voice Acting Mastery - Website and Podcast by voice actor Crispen Freeman (Young Justice, Hellsing)
Deven Mack - Voice actor and casting director (Beyblade, Dust: An Elysian Tale) - Frequently discusses voice acting experiences, techniques, and other helpful information via his social media - Tumblr Tag| Facebook
1) A Microphone - A microphone is the most important piece of equipment to purchase as it will be responsible for capturing the nuance of your voice as accurately as possible and providing your clients with a clean final product. However, as a beginner and individual (not a studio), you have a lot more flexibility in picking an inexpensive beginner mic that will allow you to get started without making any major financial commitments.
My recommendation for a beginner microphone will always be a USB condenser microphone. All this means is that your mic will connect directly to your computer via a USB cable (without having to buy a separate audio interface) and the microphone design itself lends to a crisp and clean final product. Condensers are more delicate, but highly precise and responsive to subtle changes in sound.
Here is a list of a few good choices to start with. I used the Samson C01U for over 3-4 years and recorded for a number of games and projects, including Deus Ex and Heroes of Newerth.
The good news is, is that most of what you need is going to be available very cheaply or even for free! I used my Samson along with the freeware program Audacity for over 5 years before switching over to a more powerful DAW that met my needs as an engineer better.
Here are some more good choices to start with - click the images for each program to see the website where you can get them.
There are a couple of different web sites and communities you'll likely come across - while I'll include a list of my favorites, knowing what each site can help you with is important before you invest time, energy, and resources in any particular one.
Forums, Podcasters, and Social Media Groups: Forums, podcast audio drama producers, or groups that gather via social media (such as Youtube, Tumblr, etc) will give you the experience of community. You'll find a diverse spectrum of ages and experiences, mostly creating content as fans or for fun. Projects here will vary from fandubs, to audio drama, to student animation, and indy video games. It's less professional and you may have to dodge the drama that comes with other beginners, but you may also stumble across friends and connections who are making strides into the professional realm. This is an industry of who you know, and the internet is a good place to start getting to know your industry.
Freelance Sites: Generic freelance sites typically have media sections where international or small budget clients are looking for quick, inexpensive voiceover that gets the job done quickly. It's a good place to get your feet wet in low stakes voiceover, but you have to be very quick and efficient - the jobs are usually about turnaround time instead of quality, but you can find decent clients willing to compensate your time and effort. Plus, you don't have to pay for a subscription to the site itself, though you may turn over a portion of your earnings on each gig.
Pay to Play: There are a lot of differing opinions on pay to play sites. In a nutshell, they require you to pay a monthly or yearly subscription to access jobs that are monitored and curated by the website's staff. These sites function as an automated agency and include jobs that pay better and give you more protection from scams as talent. However, the talent pool is often more experienced, making it much harder to break in if you're just starting out. Some individuals and voice types do tremendously well with these sites, others do not. If you think you're ready, try to take advantage of subscription deals that aren't an extensive commitment financially and get a feel for how they work. You may make enough to pay for your next subscription period and at the least break even from the experience.
Below, I'll link some of each type of site that I'm familiar with. Be sure to do your research, especially with pay to play sites, before making commitments, but remember to have fun with every opportunity. Good luck!
ACX University Studio Gear Review (Suggestions for Equipment)