Create a character, and imagine a problem facing that character. Daydream a scene in which the character is struggling with the problem. Then write the scene quickly, trying to capture your daydream on the page. Once you have it all down, you can go back and edit (it's normally better not to edit while you're writing your first draft). Normally, your story beginning should set up the character's struggle, and the ending should show or hint at the result of the struggle.