Rey is Palpatine's granddaughter, one of her parents is the descendant of Palpatine and gets killed off by a Sith dagger. You can see the dagger on the trailers.
Luke and Leia knew all along Rey was Palpatine's granddaughter this is why Leia sends her to Luke, and this is why Luke does not want to train her.
• Palpatine is back ON THE FLESH. He spent all this time in some unknown planet building his fleet and army
• Snoke is a puppet of Palpatine, he has a collection of failed Snoke clones in a lab.
• Rey heavily struggles with the dark side the entire movie, she almost kills Chewie in one scene by accidentally using force lighting on a ship where he was at.
• Kylo gets beaten down by Rey in a fight (you can see it on the trailers, with the waves hitting a ship). While he is laying there almost dead, Han Solo comes back as a force ghost to tell him it is not too late to come back to the light side. Kylo then throws his lightsaber away and goes to help Rey.
• After beating Kylo, Rey is scared to use the force again, because she is losing control and tapping into the dark side. Rey goes back to Ach-to, where she is comforted by Luke. Luke then raises his X-Wing from the water so Rey can join her friends in fighting the First Order
• Rey goes to battle Palpatine and Kylo goes in to help Rey. Before, however, he fights all the Knights of Ren just using the force and his fists.
• Rey and Kylo fight Palpatine, but Palps uses them both to rejuvenate himself. He then throws Kylo off a cliff, never to be seen again.
• Rey is laying on the ground almost dying until she hears Leia, Luke and some other jedi voices. She rises and deflects Palpatine's lighting back at him. He dies.
• By the end of the movie, the heroes go back to Tattoine and some random guy asks Rey who she is. She says she is a Skywalker; The movie ends with the Twin Suns