I'm listing the initial set up for the documentary as seen in the documentary previews, not the middle or end.
Cyntoia Brown was adopted as a young child from a bio mother that was a drug-addicted 16 year old. When Cyntoia was 16 years old herself, she ran away from her adopted home and would hang out with a drug dealer and pimp named Kut-Throat. Cyntoia says most of the time they were doing drugs or having sex when he didn't have her working as a prostitute.
One evening Cyntoia meets a man named Johnny Allen in the parking lot of a Sonic. After small talk Allen asked Cyntoia if she was hungry and if she was up for any action? They went to his house and had sex.
At some point after sex, Cyntoia shot Allen in the head with a gun she kept in her purse. She claimed the shooting was self defense - that she believed he was reaching for a gun under the bed. The prosecution claimed she shot him while he was sleeping so she could rob him.
After shooting Allen, Cyntoia took $172 , two of his guns and his truck.
The documentary follows what happened to Cyntoia after Tennessee charged her with Allen's 2004 murder. She was labeled a prostitute (today she would be seen as a childhood victim of sex trafficking), and charged as an adult for the crime instead of a minor.
Based on the evidence it's pretty clear Allen was sleeping when he was shot by Cyntoia, which would usually give me sympathy for him. But Allen was a Real Estate agent and a Youth Pastor - a move many pedophiles make to get the trust of the community and access to kids. (That was not part of the documentary.) Allen calling himself a Youth Pastor, while sleeping with a 16 year old girl, suggests he was a pedophile and sex predator (again, my speculation, not part of the documentary).
The documentary POV is one of sympathy for Cyntoia, skipping over other violent acts she committed as a teen. Her case became well known after many celebrities started sharing it on social media.
The documentary mainly focuses on Cyntoia's effort to rehabilitate herself and her attempt to get clemency from the Republican Tennessee Governor. Overall an interesting watch.