After the defeat of the Empire, the war is not over. Splintered Imperial forces remain active, while the Rebellion has not made a clear (or morally clean) transition to rule. There is essentially a galactic Cold War happening.
Imperial soldier FINN (John Boyega) defects to Tatooine; there he meets scrap collector REY (Daisy Ridley) and her droid BB-8
Daisy’s mentor (Max von Sydow) points them toward a larger destiny involving a lightsaber that is connected to the now-absent Jedi.
That lightsaber leads to HAN SOLO and CHEWBACCA, who take Rey, Finn and BB-8 on a galactic quest to find LUKE SKYWALKER
Luke is supposedly in exile, guarding a Sith tomb (or some sacred site) for which Finn’s lightsaber is the key
Meanwhile, an Imperial commander (Gwendoline Christie) is on Finn’s trail for defecting
A pivotal character (Domhall Gleeson as Luke’s possible son) is acting as double-agent against both the Rebellion and the Empire, in order to stop super weapons possessed by both sides
And a Darkside user named KYLO REN (presumably Adam Driver) will be hunting down the lightsaber and its wielders.