TL;DR Try your hand at writing. Read some stories in here, let your imagination wander. It's not that hard.
If you can write, you are a writer. You might worry you are not a 'good' writer, but that's subjective, and can change. The challenge is to write that first draft without editing and second-guessing your every word.
Flash Fiction is a good way to start off, as it's a short story, typically fewer than 1000 words, written over a few days. It's often done as a challenge to a prompt, such as a photo, a song, a mash-up of genres, or a random selection of keywords.
The point of these prompts is to push you a bit, to get you out of a rut, or if you're new to writing, to give you a starting point. Don't over-edit, just consider this a quick way to try out a new character or situation or genre. You may end up with just a part of a story, a scene, a fragment—that's fine. Keep it simple. Outline, structure, character arcs, plot points, clever twists--all can come later. Stuff your story in a drawer, show it to a friend, even put it online. Show it to your mother, as praise is a good thing. Then talk it over with other writers, tweak things, and the next one will be a little better, a little easier.
I used to be part of a site by the same name, here, and did 100 or so Flash Fiction back then. Some were good, some were meh, and I occasionally found a recurring character or theme in several that suggested a novel.
I'll post a new prompt here each Friday, with the FF due by the next Friday, noonish. Post your story on your blog, then link to it in the comments of the prompt.
Note - stories are copyright by the author, and they retain all rights to their work. Image from here.