You don't know the ending, or the middle, or the beginning... Just write.
You absolutely must outline before you start or outlining makes you break out in hives. Just write.
You've read every article on how to begin. Just write.
You've attended creative writing classes. Just write.
You aren't good with grammar, or spelling, or commas. Just write.
You don't know if anyone else will like your story or your poem. Just write.
You've heard it's best to write with pen and paper, on a laptop, on a typewriter. Just write.
You think of the perfect scenes as you're falling asleep or when you're on the bus or when you're sitting in class. Just write.
You feel as if you have to write or you'll burst. Just write.
Write what you want to write, where you love to write, the way that suits you, when it suits you. Write with a complete outline or by the seat of your pants, with a pen or with a keyboard. Write stories. Write poetry. Write the breathings of your heart. You can spell-check and edit, later. You can add commas and take them away, later. You can get beta readers, later. But before you do all that... just write.