Big Gete Star was created from a computer chip in space that began absorbing and assimilating debris, growing gradually larger and larger until it eventually absorbed Cooler who was able to take control of the star.
It should also be noted that the gete in "Big Gete Star" comes from getemono, the Japanese for "cobbled together".
The Big Gete Star was first seen in Dragon Ball Z: The Return of Cooler. Cooler wanted to use New Namek as a source of fuel for the star. After Goku blasted Cooler into the sun in Dragon Ball Z: Cooler's Revenge, Cooler was not killed, but severely damaged. The Big Gete star was what found his remains, and integrated them into its core. The crew includes Cyclopian Guards, thousands of Meta-Coolers, and the Guide Robo.
Dende knew of Cooler's plans, and asked the Z Fighters to stop him. Super Saiyans Goku and Vegeta engaged in a heated battle with Meta-Cooler, and they defeated him. However, the Big Gete Star housed not one Cooler, but hundreds, if not thousands. Goku and Vegeta had no chance of beating them all, and are absorbed by the Star itself, where they find the brains behind it all, the actual Cooler - an obscene and grinning head split with one remaining eye, strung up by wires and sheets of metal.
All Meta-Coolers seen previously were under remote control, and the machine itself formed Cooler's true body. He plots to drain Goku and Vegeta of all their energy for his own purposes. But their power is too much and begins to overload the capacity of his systems. The Saiyans then flood the Big Gete Star with energy, causing it to crumble and his remote-controlled dolls to self-destruct, while Cooler starts to lose his hold on the planet.
Sickened by such "scum" yet again foiling his plans, Cooler fashions a final body from what's left of his organic self, intending to throttle Goku in wires. Even to this end Cooler believes victory is inevitable, and his arrogance costs him his life as Vegeta shears off one of his mech arms, giving Goku time to destroy what was left of his body. With the "brain" gone, the Big Gete Star disintegrates over New Namek, with Vegeta crushing the original chip in his hand, ensuring that Cooler would never return.