Join the facebook groups Author Unleashed, and 20booksto50k, and all your questions will be answered by the files and experts there, BUT before you do, absorb the following advice.
It is only possible to make a profit from self-publishing if you:
(a) publish a full length good book with a great cover, several times a year in a popular genre, or
(b) write erotica or explicit romance or very violent books
AND
you work out how to become an expert in running ongoing online advertising campaigns
AND
You can afford to invest £1-5k upfront in book cover / editing / advertising costs with no guarantee thet you will recover these costs.
When you join the Fb groups above, people will be more positive than me. They will tell you that you can invest very little / write in an unpopular genre and still make a profit. This is not true.
I write in a medium popularity genre. I self-published because I could not get a book deal as my genre wasn’t fashionable enough and I didn’t want to wait years for the market to improve. An agent told me that to get a book deal you don’t need to write a particularly good book, you just need to pitch it at the exact time that publishers want that genre. You have to be lucky, basically. If I pitched erotic romance in 2011 or dystopian YA in 2012 or something with trans characters in 2019 I’d have got a book deal no problem. But I did not. (If you have a romantic fantasy book by the way 2023 is your year.)
My book has a professional genre-appropriate cover, was edited by a very senior editor from a top publisher, has numerous great reviews (average 4.9*) but I cannot sell it at a profit because adverts cost more than people are willing to pay for the book. My investment in cover art editor, ads and formatting software was £2k, plus the 100s of hours work.
I was pirated across the globe within 24 hrs of release, so you can get free copies of my work anywhere, if you don’t mind the spyware that the thieves have probably added to the book file.
So it depends what you write. I know some indie authors who make q lot of money but they all write explicit sex scenes badged as romance, or torture scenes badged as crime, or both.