On the plot level, The Tempest is about a group of sailors who shipwreck on an island. There they find Prospero and Miranda. Prospero was the duke of Milan before being exiled there. Miranda and one of the sailors fall in love, while other sailors plot to take over the throne of Naples and still others plan with Caliban, Prospero's monstrous servant, to kill Prospero.
Through magic, virtue, and young love, these plots are thwarted. The ship is repaired, and Prospero is restored to his rightful place as duke of Milan.
Now, thematically, the play is about the social order and what happens when it is upset, about the right to rule and rightful rulers, and about the wonder and magic of the world.