Origin

There are three completely different origin stories of Flash.

1. Flash aka Jay Garrick was a college student and a champ of football. One day while working in the laboratory he accidently inhaled hard water vapours which resulted in a discovery of his super speed.

2. Flash aka Barry Allen worked as a forensic scientist. He was known to be super slow and frequently late for any of the work. One night, as he was getting ready to leave his lab a lightning bolt broke a case of chemicals and spilled them all over him. He later found that he can run fast and heal so quickly.

3. Flash aka Wally West was a nephew of Barry Allen’s wife Iris West. On his tour of Central City police laboratory, Wally met with a freakish accident that exposed him to electrically charged chemicals. This gave him super speed and agility.

Superpower

Evident from the name itself, Flash can run at a superhuman speed which later gave him the ability to go beyond timeline enabling to wander in the future, the past or an alternate universe or create flashpoint. Yes, he can beat Superman in a race with ease. Moreover, his healing ability can make him stand for a long time against his nemesis or enemy.

Mission

Although all three Flash had different missions but it was more or less about defeating their nemesis or enemy. In that process, they often had to save innocent people or sometimes, world.

Journey

The DC Comic has given an elaborated version the 2^nd Flash which is Barry Allen. This young speedster continuous struggles with a memory of his mother untimed death by another speedster. In this emotional journey of discovering the real killer of his mother, he broke the timeline on multiple occasions that include the creation of a new world where his mom was alive. Due to this, there were so many flashpoints and alternate universes created that constantly gave enormous bad memories.

Reference

http://dc.wikia.com/wiki/Flash_Origins