What is the story of halo 1

It is about a war between humans and an alien race called the covenant who come across an ancient space ring which contains the "flood". The flood is a virus type thing which takes over body's turning them into zombie like creatures. The covenant believe that the only way to destroy the flood is to activate the ring and wipe out every living thing in the universe. You play as master chief who is a spartan super soldier and it is up to you to stop the covenant form activating the ring.