What are Dragonballs?
Dragonballs are 7 magical balls that only exist on Earth and the planet Namek which are made by the Earth's guardian Kami-Sama (Earth) and the eldest Namek Guru (Namek). The Dragonballs contain the power to grant any person's wish such as immortality, revive a person back from the dead or some other simple wish. Every Dragon has its limitations and cannot grant certain things.

Earth's Dragonballs
Before the Dragon can be summoned the 7 Earth Dragonballs must be collected and brought to one place. The Dragon can now be called to grant one wish. Wishes such as destroying planets aren't acceptable due to limited powers of the Earth's dragon. However it can bring back a mass amount of people from the dead. The existence of the Earth's Dragon Balls is determined by whether Piccolo and Kami are alive or not.

Namek's Dragonballs
The Namekian Dragonballs originate on planet Namek. Just like on Earth there is seven Dragonballs with a Dragon that can be summoned. To summon the Namekian Dragon the seven Dragon Balls must be collected and brought to one place with a Namek that knows the password and can speak Namekian. Unlike the Earth's Dragon, the Dragon from Namek can grant 3 wishes and can revive a person as many times as the person wants as long as the person to be revived didn't die of natural causes. One revived person per wish.