There is a paper and there is a utensil to mark the paper: a pen, pencil, crayon. Or there is a keyboard and a screen and a blinking cursor.
Start. Make a mark, throw out words, make lines, make a mess. Write every day. Practice. It takes practice and practice and more practice and reading, reading and more reading and all of that will not make the internal critic or internal editor or the internal fears go away but it can help to make your writing better, give you a sense of your own writering process and help you with your style and your unique voice.
The thousands of people out there telling you the way to writing, offering workshops and CDs and videos tell you there is a formula to being a writer and there is: it’s called writing. And to do that, you have to write and you have to restart writing, every day. You cannot be a writer if you don’t write and keep all that perfect writing in your head. It is statistically impossible to be a writer who does not write a thing. It’s safe though, except for managing the conflicted feeling that you want to write. And it also helps to protect you from your inner self who might not be able to bear the process of having your writing rejected for publication.
Of course there are people writing who are doing it because they want to be famous writers and perhaps some of those people might want to give that thought a rethink, but, that’s not you. It doesn’t matter what you write or that you don’t have fully formed story idea, or that writing prompts leave you cold or confused. Just start writing.