To begin with, there were seven Green Lantern Corps, each representing a colour of the Emotional Electromagnetic Spectrum. The further from the center of the emotional spectrum, the greater the influence a powered light has over its bearer.
Later on three other Corps were discovered, which were White, Black and Ultraviolet.
The Maltusians, the oldest known race in existence of DC Universe, were the first to discover and harness the power of Emotional Spectrum, which is an energy field that is fuelled by the emotions of all sentient beings. Their successors were eventually able to harness the power of emotions of different colours, and create the Lantern Corps DC readers are familiar with today.
All members of the Corps have Power Rings which helps them channel their emotions as different colours of light. This grants the bearers of these rings immense powers like flight, blasting energy beams, creating physical projections of anything they can imagine, and so on. The power of the Lantern Corps are only limited by their emotions which makes them one of the strongest forces in the universe.
But how did each Corps come into being? With all boasting their own complex history, it's time to dive into the stories of how all were created, from Green through to Ultraviolet...