There are four flash characters in the DC comics. Jay Garrick, Barry Allen, Wally West, and Bart Allen. So they have different ways and sources of getting powers. At first, Jay Garrick, he was from the Golden Age- later belonging ti Earth-two. He inhaled the vapors of hard water and then, massive water ti gain his superspeed. Barry Allen was from the Silver Age. Barry Allen was a forensic scientist for the police department. One day while he was working on his lab, at the same time, Star lab was making another invention called The Particle Excelerator. But unfortunately, a malfunction happened there. It blew up, scattering dark matter over the city. A thunderstorm was also happening at that time. When Barry was trying to close something on the ceiling of his lab, he was holding a metallic thing. With the thunderbolt on that metal chain, the lightning struck, and the dark matter also entered into his body. He was in a coma then. When he woke up, he felt that he has got the superpower. Because the particular piece of dark matter, made his body regenerate too much than a normal body. Thus he became the Flash and got powers. Wally West also got power like the same way Barry got. He gained power as a kid flash. It was by an identical lab accident as Barry. He went to visit Barry, and Barry recreated the cabinet of chemicals to make Wally understand the whole thing. Then suddenly, lightning struck that coated him in energized chemicals was vanishingly unlikely. Wally got a costume and got the name kid flash. Bart Allen got his powers by born. Because he has the blood of previous two flashes. His father, Don Allen, was the son of Barry, and his mother was Meloni Thawne. Thus he inherited the power and ability and became the last flash.