You have to create the conditions to write. Carve out some time to write, then start writing. Use the little moments in your day when you're not doing anything.
Or, sit at your computer, and write for one hour, take a break, then write again for another half hour or so. It doesn't matter if it is good or not. Just plough ahead.
When you want to write a book, reading helps you figure out what you like. Reading good writers can help you make your own voice better.
Some writers plan first. Other writers just jump in and wing it. Some writers are in-between planning and winging it.
You don't need to know which kind of writer you are when you're starting out. Just try something and see what works for you.
Writing can be really hard. When you're stuck, call up a friend with a different way of thinking, or talk to a friend who's writing a book to help you think through the issue in your book.
You can also reach out to other writers that can provide support. One way to find them is to read the acknowledgements in books.
A writing group or accountability partner can help provide perspectives that aren't your own, and tell you when you've gotten something wrong.
Maybe your prose is clunky, or your character depictions are not good, or stereotypical. Learn to accept criticism with grace and humility.
What makes you a writer is the fact that you ...write. Believing you are a real writer will give you power on the page.