ABA is an underlying structure used in many “moving arts”.
In a story, it looks like this…
Characters
There’s a main character. They have a goal. They reach the goal or they don’t. If they don’t there are still lessons learnt.
There are secondary characters. The secondary characters want to support or block the main character from reaching their goal.
Plot
The first plot point, A, is where the story begins.
The main character is in a certain place - A.
The final plot point, also A, is where the story ends. This is the same place the story began (hence it also has an A).
In the middle is B, which is everything that happens as the main character pursues their goal.