I remember a time when only labels & distributors could do it, and it was a very unknown world. I personally love the website Distrokid.com for self-releasing.
This makes is easy to get your music on all of the platforms, BUT it also lets you split your shares with other writers/publishers and DISTROKID handles the splits! Trust me, you DO NOT WANT TO HANDLE ACCOUNTING for the lifetime of a song, it's no fun!!
I always used to joke that making a song with someone is like having kids with them, and you share custody forever! There are other great resources like cdbaby, and if you know of some that you like using, please let me know!!