Ring | Dragon Ball

Dragon Ball Z (from fandom Dragon Ball Wiki)
Dragon Ball Z follows the adventures of the adult Goku who, along with his companions, defends the earth against an assortment of villains ranging from intergalactic space fighters and conquerors, unnaturally powerful androids and near indestructible magical creatures. While the original Dragon Ball anime followed Goku through childhood into adulthood, Dragon Ball Z is a continuation of his adulthood life, but at the same time parallels the maturation of his son, Gohan, as well as other characters from Dragon Ball and more. The separation between the series is also significant as the latter series takes on a more dramatic and serious tone. The anime also features characters, situations and back-stories not present in the original manga. 

Dragon Balls
The Super Dragon Balls are the original set of Dragon Balls, created by Zalama in Year 41 of the Divine Calendar. These Dragon Balls are the size of planets, and their star marks remain the same no matter from what angle one looks at them, which was patented by Zalama in Year 42. Each ball has a diameter of about 37,196.2204 kilometers (which puts their volume just under half that of the planet Neptune). To summon the Dragon of the Gods, one must chant, "Come forth, Dragon of the Gods, and grant my wish pretty peas!" ("Come forth, Divine Dragon, and grant my wish, peas and carrots!" in the Funimation dub) in the language of the gods. After a wish is granted, the Dragon Balls are scattered throughout both Universes 6 and 7. Granting a wish drains the Super Dragon Balls of their light, and in order to grant another wish, one must wait the lifespan of a cockroach (one year's time). The Super Dragon Balls are the strongest known set of Dragon Balls as the Dragon of the Gods can grant quite literally any wish with no limitations, though the dragon can only grant a single wish per summon. While Goku Black and Future Zamasu were able to destroy the Super Dragon Balls, it is unknown whether they were able to do so with their own power or by making a wish to Super Shenron, leaving the true durability of the artifacts a mystery. Nearly everything that is known about these Dragon Balls is due to the wisdom of the all-knowing Zuno.

Earth Dragon Balls
Like most other types of Dragon Balls, there are seven in existence. When all are gathered, they summon an Eternal Dragon named Shenron, who can grant any wish that doesn't exceed his powers. Once used and Shenron fulfills the user's wish, the Earth Dragon Balls are turned into stone and then scattered to different random locations on Earth, rendering them useless for 365 days before they can be used again.

The limitations of Shenron's power are tied directly to the power and abilities of his creator (Kami, and later Dende). Amongst the rules that have been observed to restrict wishes granted by Shenron are that he cannot:

Revive a person that he has revived once before.
Revive a person that has died more than one Earth year ago.1
Kill a person whose power exceeds that of his creator.
Grant the precise same wish twice.
Revive a person who has died of natural causes, including disease and old age.
Create true love or force a person to fall in love.
Make a person substantially stronger than their current limits.2
Transform a Biotechnological Type Android back into an ordinary human being.
Make a wish in bumping the limitations of his power like locating a Super Dragon Ball in another universe.

He will, in general, grant wishes regardless of the morality of the wish or its consequences. However, wishes can be denied at Shenron's discretion, usually due to foreseen limitations of the wish like locating an object in another universe. For example, Shenron may warn against a wish to revive a person which would put them in a position that would cause them to immediately die again making a impractical wish. As in the case of Frieza's revival, he may still grant the wish if the wish-maker confirms that they are accepting of these consequences. Shenron can suggest the summoner to make a new wish in place of the wish he cannot grant.

Before, Shenron was only able to grant the user one wish per summoning, but after Dende re-creates him and the Earth Dragon Balls, Dende upgrades Shenron to grant the user a maximum of three wishes (two if multiple people are revived with one of the wishes).

When the Dragon Balls are turned to stone and scattered, the exact star count is preserved, meaning a user could catch a specific ball before it scatters, and it would retain the expected number of stars.

(from fandom Dragon Ball Wiki)