Step One: Grab a computer/laptop/tablet/cell phone/pen and paper/stone and chisel/stick and patch of sand. Whatever you like.
Step Two: Find a position that allows you to use your chosen writing implement(s)/device(s) comfortably. Sit, stand, lie flat, hang upside-down, it doesn’t matter.
Step Thee: Write.
There is no one way to write correctly. Some people may tell you otherwise, but they’re wrong. If you write, you’re a writer. Some people write every day, some people don’t. Writers can write novels, short stories, poems, blogs, articles, haikus, obituaries, limericks, or shopping lists. As long as you’re writing, it doesn’t matter. Some people make outlines, some wing it. Some start with “Once upon a time” and keep going straight until “The End.” Others write out of order. Most people rewrite their opening at some point. Some people listen to music, some prefer television, and some need absolute silence. All of those things are okay.