Fifty words are a paragraph, maybe 5-7 sentences.
It is a bit of description, a thought, or a beat of action or dialogue.
But they add up. String a few of those together, and they form something more significant—a scene or maybe the first primary story beat of a short story.
String those together, and they become the first act or the whole story.
A story works as a fractal, and the micro reflects the macro.
But if you are looking for a place to start, begin with fifty words and then build it out from there.