Earth's Dragon Balls:
Dragon balls. Well I guess they are pretty important because the series is named after them. In fact the Dragon balls are very important. I can't count how many times they have saved Goku and his crew. All together, there are three different kinds of Dragon balls. When you collect all seven, a eternal dragon appears and grants either one to three wished. Kami made the Dragon balls after he separated with his evil half. The earths Dragon balls were about the size of a baseball with red stars incased in the inside. When all seven Dragon balls were brought together, a special chant would awaken the eternal dragon.."Come out Shenlong and grant my wish." The dragon would appear and grant a wish to whoever asked. After the wish was granted, the Dragonballs would scatter across the world, and turn to stone for one year. The Dragon balls can only be on Earth as long as Kami is alive, and since Kami and Piccolo are the same person, if Piccolo dies, Kami dies, and this happened once. When Piccolo and Kami died, the Dragon balls turned to stone until Piccolo was brought back to life. Another time the Dragon balls turned to stone was when Kami and Piccolo fused, but Goku asked Dende to take over Kamis place, and the Dragon balls were restored. Dende was able to change the rules and the earth Dragon balls were able to grant two wished instead of one.
Its is revealed in DBGT that the Earths Dragon balls generated seven Evil Shenlongs. It is told that with each wish that was made from the Earths Dragon balls, two different types of energy were created; a plus and minus energy. All of the minus energy's that were created formed the Evil Shenlongs.
Namek's Dragon Balls:
The Dragon balls of Namek are quite larger then the other two kinds of Dragon balls. They were created by the Eldest Namek and were able to grant three wishes to who ever obtained all seven. The name of the eternal Dragon that occupied the Namekian Dragon balls was Porunga. To call out Porunga, they have to chant out the phrase, "Takaroto Popporunga Pupiritoparo" in the Namekian language. After the wishes were granted, the Dragon balls would scatter around Namek and turn to stone. Later in the DBZ series, the Namek people were able to upgrade Porunga making him much stronger and able to grant wishes that he couldn't have before the upgrade.
Black (Drark) Star Dragon Balls: The Black Star Dragon balls were only seen in the DBGT series. They were created by Piccolo the Demon King (Piccolos father). The Black Star Dragon balls were much more powerful then any other Dragon balls and had black stars on the inside instead of red. The Black Star Dragon balls could only grant one wish, and when the wish was granted the Ultimate Shenlong would appear. After the wish was made, The Black Star Dragon balls would scatter all across the universe. When a wish was made from the Black Star Dragon balls, its power was so great, it caused the Earth to self destruct. The Dragonballs had to be collected to counteract the Black Star Dragonballs effect. In each Black Star Dragonball, was a Evil Shenlong.