Halo Central is a large orange building that floats through space. It is the HQ of the dudes who made the Halos, and where people go when they have Halo business to do.
Halo Central is what was built when the guys made halos. They decided it was difficult to stand out in the middle of space while they build halos, so they made a large factory that had Oxygen so they could make the halos. They put them together in what was eventually known as Halo Central.
After the maker guys died, Halo Central just floated in space for thousands of years. Eventually, Master Chief discovered it when he flew into it with his spaceship. His spaceship blew up, and he crashed in through the roof. It just happens, he discovered it right when some aliens were trying to use it to blow up the galaxy.
Master Chief took out his Spartan Laser, and blew up all of the aliens and blew up Halo Central. Halo Central has since re-constructed itself, and it once again floats around space randomly.