If you want to sell your music online besides having the option of creating individual accounts on iTunes, Google Play, Amazon and Spotify and post you song on each of the 4 platforms.
An easier option is to create a DistroKid account and post a song for free.
Once you upload your song you will be payed monthly and the best part is that you keep 100% of your royalties.
After you have tried DistroKid with one of your songs, is you are satisfied, you can upload an unlimited number of songs for only $19.99 per year.
DistroKid is one of the best music selling services out there, having already been praised by Forbes, HypeBot, TechCrunch