Obviously you can’t publish anything if you haven’t written the words down. But writing a book, especially a fantasy novel, is not only writing words on a blank piece of paper.
There is a lot of thinking involved. You need to spend time with your characters and get to know them. Some may do this also through writing; by writing scenes they know will not be in the book, but they simply serve as getting to know the characters and figuring out how they behave and talk. Others may choose to play with their imagination, have arguments with the characters in their head.
Then you need to do world building, which is when you create the fantasy world and invent the “laws of physics” the world adheres to. If you have demons running around, then the question becomes where do they come from and how did they get here? And if you want to write something original, it may take even more time to figure out how it all works.
Another aspect is research. If your main character is a police officer, understanding how police investigations are done can help you build a good crime story. Sometimes you may want to experience the things you’re writing about, such as shooting a gun or parachuting out of plane instead of simply imagining what it feels like. [Obviously, without hurting yourself or others.]
All along the story you do research; to take the example again of shooting, how many bullets can the gun shoot? How accurate is it at great distance? If a character gets shot in their leg for example, how much blood leaves the body? How long until they pass out? Do they pass out or does something else happen? How long until someone goes into shock?
Writers get stuck a lot. At least that’s my case. Sometimes it’s a big block and I can’t write at all, other times it’s a small open question I need to remember to resolve within the next few chapters. What helps is distraction and inspiration. Watching movies or series, listening to music, and reading books can stimulate your inspiration. It doesn’t mean you copy someone else’s work, but maybe you realize your book doesn’t have enough tension. Or you would like to have more characters in your book. Maybe you love the dynamic between two characters in a series, but you would have given them a different twist. You can draw inspiration from many (even unlikely) places.
4. Post production
After you’ve written the story, there is a lot editing and re-writing involved. But even after the book is done, you still need to figure out book cover, title, series name if it’s a series, dedication, acknowledgements, book format, launch date/time, marketing platform & social media use, self-publishing or traditional publishing, pen name or real name, and I’m sure I’m forgetting others.
Writing a book is more complex than it seems from the outside, but it’s a challenge worth taking on.