Without structure you have no story. Structure in story must include a character in a situation with a problem who tries over and over again to solve that problem but fails again and again and then, at the climax of the story, makes a final last-ditch-effort attempt and proves himself or herself. Within this framework, you have plot or story arc and character arc.
Joseph Campbell's HERO'S JOURNEY contains the best story structure formula and is used by novelists and screenwriters.
1. The hero is confronted with a challenge,
2. rejects it,
3. but then is forced (or allowed) to accept it.
4. He travels on the road of trials,
5. gathering powers and allies, and
6. confronts evil—only to be defeated.
7. This leads to a dark night of the soul, after which
8. the hero makes a leap of faith that allows him to
9. confront evil again and be victorious.
10. Finally, the student becomes the teacher.
Every book or film can be analyzed according to the Hero’s Journey.
Once you learn to plan a story this way, it becomes much easier to plot stories and to critique your own work as well as the work of others.
Basically what's happening in story is a character must make a CHOICE and this choice is shown by ACTIONS and all those actions must have CONSEQUENCES.
The character must make a choice required by the story and there must be action because of this choice. Think CAUSE and EFFECT. Something happens, the character reacts based on who he or she is and that causes reaction and so on. There's a SET-UP, a RESPONSE, an ATTACK, and a RESOLUTION. This paradigm will make it easier to structure your story.
The MAIN CHARACTER or PROTAGONIST or POV NARRATOR has a history (the character sketch and backstory you've created) and something changes that creates the story: a bomb drops, a best friend betrays, an opportunity arises, etc. The hero attacks the problem or goes after the goal and something else changes and then, finally, things resolve: the mountain is climbed, the treasure is found, the race is won.
Story is like life. As heroes of our own stories, we are constantly responding, reacting, changing, adapting, shifting and, because of our actions, something changes.
That brings about conflict and that is story.