Understanding where Black Lightning's powers came from involves knowing where you first started reading/watching his stories. When he first came onto the scene in 1977, he used technology to harness the tremendous power of electricity (via Distractify). He receives a belt from Peter Gambi, and it's the belt that gives him his abilities, meaning when he's not wearing it, he's powerless.
Over the years, this origin story became simplified. Instead of wearing a belt, the comics changed Black Lightning's origin to be a metahuman, meaning he was born with his powers. He possesses the metagene, and anyone who has that component in their genetic makeup can access a wide breadth of powers. For this reason, Jefferson Pierce can pass down his powers to his daughters — Anissa and Jennifer — who also become electricity-based superheroes.
The CW show added an interesting wrinkle to his origin story. In the series, Jefferson (Cress Williams) is born with the metagene but doesn't immediately have superpowers. Those only develop after receiving a vaccine, which was part of a massive program by the American Security Agency to create metahumans. While Jefferson gets powers, many other children died due to the experiment in a haunting storyline that mirrors the Tuskegee syphilis experiment.
