Relatively canon up through the last ten minutes of The Miller’s Daughter.
The dying Rumplestiltskin returns to Storybrooke only to find Cora attempting to kill him with his own dagger. Hoping to kill her instead while remaining technically blameless, he suggested a candle of dark magic to Snow White that would trade his life for Cora’s. However, he was not fully honest with Snow, and had the antidote to the poison in his shop the entire time.
Snow, believing there to be no other option, goes to Regina’s vault to curse Cora’s heart. She is intercepted by Regina before she gets the chance to use the candle, and instead gives Regina the heart, which she returns to her mother’s chest. Cora lives, and so Rumple is forced to use the antidote instead.
He then returns Belle’s memories, and the Charmings decide it’s time to head back to the Enchanted Forest. So they use the magic beans that Anton and the dwarves had been growing, and take everyone back to the Enchanted Forest. Snow, Charming, Emma, Neal, and Henry move back into their old castle. Regina and Cora move back into Regina’s old castle, but is not re-instated as Queen of her old kingdom.
A few weeks after their return, Snow, thinking she can try to bring everyone together and check on the whereabouts of her subjects, holds a party to celebrate their return.
This is where our story begins.