Hi, kids! Wanna reduce art to a formula, and generalize the entire history of narrative structure with me? Cool!
A story is the chronicle of someone who wants something badly, but has trouble getting it. This establishes a conflict that (ideally) squeezes empathy out of us.
The "someone" is called the protagonist.
What they badly want is called the objective.
The trouble preventing them from getting it is called the antagonist.
A story has a beginning, a middle, and an ending.
The beginning introduces the protagonist, objective, and antagonist.
The middle escalates as the protagonist struggles to overcome the antagonist in order to achieve the objective.
The ending resolves when the protagonist either succeeds or fails to achieve the objective, and we're satisfied with the results.
But be warned...
...stories can get waaaaay more complicated.
For one thing, this structure exists in all sizes--from sagas to stand-alones to arcs to sequences to chapters to scenes to beats. The following GIF from One Hundred and One Dalmatians is just as much of a story as all seventy-nine minutes of the movie.
That movie's a hot mess.
What's more, the elements are flexible. They can be reorganized or implied or replaced altogether--but they're always there. If they're not, then it's not a story.