How are Workers in the bee hive able to make eggs into queens?

There is no difference between the eggs, it's all down to feeding.

All larvae are fed royal jelly -- a secretion of the mandibular and hyperpharyngeal glands of worker bees -- for the first three days after they hatch from the egg. After this period worker bee larvae are weaned on to a mixture of honey, pollen and a steadily reducing amount of royal jelly and they are fed on this until they pupate.

Larvae intended to become queens are fed on pure royal jelly right up to pupation. It is this different diet that makes the larva develop into a queen.