Be careful not to confuse “back story” (information needed to explain the characters personality and problems to the readers), with current plot action. Whatever has happened before the real action begins is “back story.” Be careful not to confuse explanatory action, with a plot turning point. A plot turning point is always when something CHANGES. Backstory has always been there and does not change.
Backstory is where "Telling" becomes a GOOD thing. You don't have to SHOW every little thing. Put the backstory in narrative and get on with the action.
To use a classic example, in the story Cinderella her mother’s death and her father’s remarriage are all “back story.” The mean way the rest of the family treats Cindy is explanatory action used to set up the objective. Because the Objective for Cinderella, is that she wants to go to the ball. Until Cinderella decides she wants to go to the ball nothing has really happened in the present, everything is going on as usual.
Remember, plot always happens when something changes. When the character knows what he or she wants, that is the objective and the knowing the objective is always the beginning of the story, the beginning of the plot. Now the character has a problem to solve – how to get what s/he wants. Once there is a problem statement, it’s time to get on with the story.
If there is no problem, nothing is happening, and there is no story --only backstory. Stories are about overcoming something, usually the difficulties set up in the backstory. If there is no “overcoming” then there is no satisfaction to the reader at the end.