So you ask what the hell are the Dragon Balls?
The Dragon Balls play an important role throughout Dragon Ball, Dragon Ball Z, and Dragon Ball GT. The Dragon Balls are a collection of 7 spherical, goldish balls each numbered with stars. When someone collects all seven Dragon Balls they can summon the dragon who grants them anywhere from 1-3 wishes, depends on the creator. When the creator of the Dragon Balls dies the Dragon Balls turn to stone until a new creator revives the dragon.
Kami-sama's Dragon Balls: Kami-sama created the Dragon Balls for to give humans a light in the tunnel. Piccolo Diamaiou took advantage of this when he killed Shenlon, the dragon of the balls. Kami-sama revived the dragon for the goodhearted humans. His Dragon Balls can wish infinite numbers of persons at a time but can only wish back the same person once. They only have one wish before being scattered around the world and they can only be used once a year.
Dende's Dragon Balls: During the Cell Saga Piccolo and Kami-sama merge to become more powerful, therefore the Dragon Balls disapeared. Goku finds New Namic and Dende volunteers to be the new god of earth and revive the Dragon Balls. He modifies Shenlon a bit so it can grant up to 3 wishes and it can bring any one person back multiple times.
The Dragon Balls in Dragon Ball GT vary a great deal from the other ones. They were created before Piccolo and Kami split into themselves after merging to try and gain an advantage over Cell. He creates the Black Star Dragon Balls and they are the most powerful Dragon Balls created. Instead of scattering across the world after being used they are scattered across the universe and the planet that the 'Balls are used on must have the 'Balls returned to the planet within one year or it will be destroyed.