This question has been asked of me ever since launching this project, and the answer is more convoluted than you might think. Anyone can write a book or a novel, but it all depends on how much effort you put into it.
This post will review the basic procedural aspect of self-publishing a book. These are not universal rules but essential guidelines if you want your book to be the best it can be.
The first step? Write something. Anything. Literally anything at all. Everyone has a story to tell, but it's another thing to put on paper. Don't get discouraged if you don't have all the ideas for your novel immediately. When I started writing ORION, I began with a prologue and had no intention of making it a story about a veteran and his struggles. It morphed into it, and after a while, once I had a clear idea of the plot structure, I ran with it.
Don't concern yourself with if you wrote the perfect words or sentences. Don't worry if your grammar is perfect either; these are all things you will go through during your many rounds of self-editing. (Mine was 5 in total before I sent it to a professional editor for review.).
The important part is to get your story down because the first draft is just you telling yourself the story.
Once you've written a rough (and I mean REALLY rough) draft of your story, then you should focus on the developmental editing. Look for plot holes, confusing character arcs, structure, etc. and fix those by adding, subtracting or editing chapters.
Then, once that is done, go to the beginning of your book and admire how shitty your writing is (and it will be shitty). That's ok because you're doing this to improve it! This is the time when you do your first round of self-editing. Read through the entire book and polish up the grammar, spelling, overused words, synonyms, etc. It helps if you read it aloud, as it will let you feel how natural it sounds.
Then do it again.
And again
And again
And again... Do this until you think you have done the best you possibly can with the skillsets you have.
The next step (in my process, at least) is to send it out to BetaReaders. This is someone who will read the novel and essentially write a book report about it. This will give you an honest opinion of the readers' reaction. They should tell you about things they liked about the book, something they didn't, things they wanted to know more about and all other viewpoints a reader would have.
You can then use this to make some changes to your manuscript. After sending it to my BetaReader, I added two more chapters and some paragraphs in others to solve the questions that the reader (and others) may have. It was beneficial. Luckily for me, It was more positive than negative, and I didn't have much to change.
That's another thing. Don't use family or friends. As easy as it is to ask, you will not get an honest opinion about it because clearly, they are biased with their love for you and want you to succeed (hopefully.).
So find a BetaReader that has done it before and is brutally honest about their reviews. GoodReads.com is an excellent place to find them.
Then, find a professional editor. Get quotes and timelines, and negotiate the price and details. Ensure you're getting the correct type of editor because there are many different kinds. (Copy editor, Line editor, Developmental editor, etc.) This is a whole other blog post in itself.
This is the stage that my book is at right now. Once you have dealt with the editing process and your book is formatted correctly, you can use one of many self-publishing services. I'll be using Amazon. Create your book cover (I made my own, but you can hire for that too.). Upload your manuscript and roll through the details of publishing through their website.
That is my process of what I went through (and currently am) to write and publish a book. There was a lot of trial and error and a lot of research to figure out how the fuck I get from point A to point B, but patience and commitment helped push me through it.
Hopefully, this answers some questions and gives a behind-the-scenes glimpse into my personal experience with the basic procedures of self-publishing.