Once you've protected your work and created your social media presence to build your fan base, you can now begin distribution through the various online outlets available. As an independent artist, you will soon realize that there is great responsibility in managing the various aspects of your career. The use of International Standard Recording Codes (ISRC) and Universal Product Codes (UPC) become a very important topic in relation to the distribution of your music, you should begin to familiarize yourself with these terms. I'll post more about the ISRC and UPC codes in short order, as there are a number of ways to retrieve them. There's also the headache of having to embed them in your audio and video files, which, although it may be a process, is most certainly worth the time to research. For the artists who want to put more focus on their music and not get too caught up in the technical aspect of things, there are a few digital distribution sites which offer ISRC and UPC codes through their services.
CD Baby is the first and one of the biggest independent digital distributors in the world. They've been around for a long time and with over 300,000 artists signed up to their service, they've proven that they won't be going anywhere anytime soon. They offer CD and vinyl distribution in addition to digital distribution. When an artist registers a single or album with CD Baby, CD Baby can issue a UPC code ($5 for a single & $20 for an album), which you can't distribute a single or album without. They charge a 9% commission for their services, but for many artists, its worth it. The cool thing about CD Baby is the fact that you only have to sign up once, after which you only pay for publishing.
TuneCORE is also one of the largest digital distribution services available online, although they differ slightly from CD Baby. TuneCORE members must pay a yearly subscription fee, but on the other hand, they don't take any commission from the artists sales.