One word at a time—it's all you have to do. It's more than enough. You can make a start whether you have a fully formed outline or just the wisp of a thought. Either approach works. One word at a time—it's all you have to do.
Your first draft might meander somewhat aimlessly; don't be overly concerned.
You may even abandon the first idea and move on to a new idea. But then you may find you have determined a way to bring the random threads together.
Overplanning before beginning writing risks blocking opportunities for discovery and surprise.
Whatever gets you through, putting a beginning, middle, and end down on paper is a perfect approach to crafting your story.
I advocate an exploratory, organic, and above all, playful approach, not because it's the only way to draft a story, but because it's the most enjoyable way I know.
Learn to be comfortable with leaving gaps or unknowns along your pathway to a completed story.
Coming back to fill in those gaps most likely results in a much tighter and more compelling story - regardless of the total words you've written.
Even this short post is close to 300 words, which is perfectly fine and adequately ambitious for your initial stories.
Go ahead and make a start. One word at a time—it's all you have to do.