These papercrafts are seven Dragon Balls, the namesake artifact of the Dragon Ball series, the paper models created by Juke. Dragon Balls are orange, crystalline spheres with the ability to call forth the Eternal Dragon Shenron who has the ability to grant wishes to anyone who gathers all seven of them.
Dragon Balls come in sets of seven with each ball containing the number of stars that signifies its respective number in the set. It was said by Colonel Silver that the Dragon Balls are unbreakable when he dropped a fake Dragon Ball. Vegeta probably did not know this when he ordered Krillin to destroy one before the Ginyu Force took them on Namek. In the Fusion Saga, while Super Saiyan 3 Gotenks is fighting Super Buu, Piccolo says "If you break even one of the balls they can never be used again", which may mean that they are not completely indestructible, though the balls were turned to stone at the time, so that might have been the cause for the warning.
Dragon Balls are difficult to find because they are scattered all over their respective planet, and are deactivated for a year after every wish, disguising themselves as stones. To have the opportunity to summon an Eternal Dragon, one must travel all over the globe to retrieve them. As technology eventually progressed, this became somewhat easier, and became relatively simple with Bulma's invention of the Dragon Radar. Though the Dragon Balls usually scatter across the Earth after having been used, Goku stops this from happening once by jumping into the air and catching the Four-Star ball before it can fly away at the end of the Fortuneteller Baba Saga.
Restrictions on the Dragon's powers are set by the relative capabilities of the Dragon Ball set's creator. A big problem throughout the series is that with any set of Dragon Balls is that their creator must be alive for them to function, otherwise they will be stones for eternity, such as in Future Trunks' alternate timeline, due to Future Piccolo's death; this often results in the Z Fighters protecting their creator with their lives. The Dragon Balls are inactive if the model of the dragon breaks; if the dragon is destroyed, the model breaks.
Without a model of the dragon and a set of Dragon Balls, it would take about 100 days to create the Dragon Balls. If the creator allows it, the Dragon Balls can be used even if a year has not passed; this happens only once in the series, when Kami allowed Goku and his friends to revive all people killed by King Piccolo, even though it had only been a few days since King Piccolo wished to restore his youth.
Since all seven Dragon Balls must be brought together, it is often a sound strategy employed by the villains of the series to find one Dragon Ball and hold on to it, while the Z Fighters go through the trouble of finding the other six, after which the villain will step in and steal them. Since this strategy technically works, but is considered cheap, the Z Fighters do not usually employ it, as they prefer to fight fair.
Old Kai once warned the Z Fighters not to overuse the Dragon Balls. This is elaborated upon in the Shadow Dragon Saga of Dragon Ball GT, since the Dragon Balls are only supposed to be used once every 100 years.
The most well known Dragon Ball is the Four-Star Dragon Ball, being the one Grandpa Gohan had and which Goku kept after he passed away, also being the one which Goku put on his first son Gohan's hat. The Namekian Dragon Ball Vegeta stole, and that was later stolen from him by Gohan, was also the Four-Star Dragon Ball. In Dragon Ball Z: Broly - The Second Coming, the Four-Star Dragon Ball is the last Dragon Ball to be collected before Trunks, Goten and Videl summon Shenron, and was also the last ball to be found by Bulma before summoning Shenron to wish back those who were killed by Majin Vegeta at the 25th World Martial Arts Tournament. In the Black Star Dragon Ball Saga of Dragon Ball GT, the first Black Star Dragon Ball collected is the Four-Star. Later, in the Shadow Dragon Saga, the only good Shadow Dragon, Nuova Shenron, is the Four-Star Dragon Ball Dragon.
In the Dragon Ball: Bouken Special, the Dragon Ball manga author, Akira Toriyama, explains that there are seven Dragon Balls because there are eight balls in Hakken-Den, a famous Edo-era Japanese novel, and that he would have hated for them to be exactly the same number, so he had the Dragon Balls be seven.
Unlike other forms of fiction that involve wishes being granted, the Dragon Balls seem to grant a wish exactly as the wisher imagined it, rather than warping the wish so that it is technically granted, but ends up making the wisher's life even more difficult. For example, when King Piccolo wished for youth, he was not reduced to an infant, but rather, appeared in his prime. Also, when a victim is revived from the dead, they are not undead, but rather, are truly alive. This is likely so that there is a legitimate reason to pursue the Dragon Balls by the protagonists, as they would not have a justification to rely on them if they knew they would never grant a proper wish. Also, unlike wishes in other literary works, Shenron is actually a sentient being; he may be capable of interpreting a wish however he sees fit, but chooses to interpret them how he knows the wisher actually wants, as a courtesy rather than as a rule. Credence is lent to this theory in the movie Dragon Ball Z: Fusion Reborn, where Shenron was asked to move all the dead people back to the Other World. He claimed that he was perfectly capable of granting the wish precisely as it was uttered, but he knew what consequences the Z Fighters were expecting, and warned them of the futility of the wish.
You can download the papercrafts here: Dragon Ball - Dragon Balls Free Papercrafts Download