The wishes are created by the Dragon of the Dragonballs.Shenlon is the Earth Dragon.Once you have all seven you normally get 3 wishes but in the Android Saga they only get two on Earth so they can revive all the people that Cell destroyed.
They have been wished to bring Krillin back fromt he dead from Namek and to revive all the people Freeza or Vegeta killed on Namek.There are many more wishes and more to come to this section.