Barry Allen, the Flash, is a brilliant detective working for the police department of Central City. When a particle accelerator exploded, it gave Barry superhuman speed, which he uses to fight other superhumans, some created by the particle accelerator explosion, some through other means.
Kara Danvers, Supergirl, is one of the last survivors from Planet Krypton. Her unique physiology gives her superhuman strength, superhuman speed, invulnerability, heat vision, freeze breath, x-ray vision, and the ability to fly. She uses these powers to protect National City from anyone that may threaten it.
Oliver Queen has trained his mind and body to perfection after being stranded on a deserted island. After spending several years as the non-powered superhero the Arrow, he has now become the Spectre, an agent of God's will.
Kate Kane, Batwoman, also doesn't have superpowers, but she has also honed her body and mind to perfection. Using a wide variety of weapons (boomerangs, shurikens, tasers, smoke bombs, a grappling hook), she protects Gotham City from the forces of evil.
Jefferson Pierce, Black Lightning, has the natural ability to create and control electricity, which he uses to fight against crime and corruption and to protect Freeland from all threats.
The Paragons are willing to work together to protect the Arrowverse from a threat big enough that requires the combined forces of all four of them.