The story of Brightburn goes like this. A couple discovers an otherworldly baby in a crashed spaceship. They raise Brandon, not knowing what he truly is. As he gets older, he starts to realize he has powers that are far beyond normal. He becomes increasingly isolated as he can't control his powers well at first. But then, instead of learning to use them for the greater good, he turns them against the people around him. He has a sense of superiority and entitlement. His heat vision is used to burn down a barn when he's angry, and his flight allows him to stalk his victims. Eventually, he descends into full - fledged villainy, making Brightburn a very different kind of super - powered story compared to the traditional heroic ones.
One key event is when Brandon discovers his super strength and accidentally breaks things. Another is when he starts to get bullied at school and his anger builds. Then there's the event where he kills his aunt. Also, when he uses his heat vision for the first time in a menacing way is important. Finally, his full turn to the dark side is a crucial event.
No. 'Brightburn' is a fictional horror movie, not based on a true story. It takes the concept of Superman's origin but twists it into a dark and terrifying tale.