This is very common. A lot of people that think about writing get kind of stuck here.
To move forward, learn to differentiate between an idea or a situation and a story.
An idea is a squirrel is bitten by a radioactive prostitute. That idea could be turned into a situation by adding 'Hilarity ensures.'
Ideas and situation aren't enough for a story. Unfortunately, there isn't just a single formula to create a story, and in darkness bind all other ways of recognizing something that is a story from something that isn't a story.
Speaking solely for myself, I try to focus my story creation efforts around Motivation-Goal-Conflict. I've found if I do that, I can express my ideas as stories and recognize if it works.
Most stories that engage the imagination have a character that wants something for a tangible reason. That's the goal (the want) and the motivation (the reason). Then, when there is something preventing the character from getting what they want, that's the conflict. It's really important because it raises the stakes and creates tension and resonates with the audience. We've all wanted something we couldn't get and felt frustrated or annoyed or angry or whatever.
That is how M-G-C works on our psyche to engage our story telling minds -- as both the author and the reader.
The part that I find is interesting is that pattern -- M-G-C -- is fractal. To overcome big conflicts we set smaller goals to get something we need and there is always something interesting in the way of that intent. If someone wanted to they could use that pattern over and over to build up a very complex story from chapters and scenes all structured around the same pattern.
Anyway, that is just one way to imagine stories. There are many other ways look at storytelling -- Save The Cat, Freytag's Pyramid, 3-Act Structure, The Hero's Journey.
The take away is that the art of storytelling is just as important and just as challenging as is craft of writing. Things like theme and symbolism fall in place, usually serendipitously through the creative act. Once you've finished your first draft, then you can start looking for the symbolism and theme opportunities that lay within the work.