On Role of a Publisher see:
https://en.wikipedia.org/wiki/Publishing
On Self Publishing, see
https://en.wikipedia.org/wiki/Self-publishing
https://www.amazon.com/gp/seller-account/mm-summary-page.html?topic=200260520
Caveats on Self-Publishing: see
http://writerunboxed.com/2016/01/19/the-perils-of-self-publishing/
http://terribleminds.com/ramble/2011/12/12/the-precarious-portentious-perils-of-self-publishing/
https://www.theguardian.com/books/booksblog/2016/mar/21/for-me-traditional-publishing-means-poverty-but-self-publish-no-way