literally what is confusing about cheryl learning that her ancestor was burned at the stake by the ancestors of her aquintances who didn't immediately apologize because they were trying to reincorporate the town at that exact moment, so she starts getting crazy into witchcraft because her ancestor was likely a witch, so she takes revenge against Archie SPECIFICALLY by cursing everybody in town so they will inevitably need her help uncursing themselves and accept her conditions for help unbeknownst to the fact that she cursed them in the first place, and then at a fall festival cheryl is hosting she gives archie a pie filled with the sins of the town which he eats before having sex with betty who is then immediately confident that they have concieved a child even though she had just recently recieved the news that she's infertile, and it turns out that the condition Cheryl had everybody accept for her help was that they would bear witness to Cheryl cutting out Archie's heart to magically heal the towns people. Also part of this happened in an alternant reality of Riverdale called Rivervale where everything is the same except that archie and betty presumably didn't die from a bomb Hiram placed in Archie's house because his fate in this reality was to get the judas kiss in the form of his best friend jughead telling him i love you during a pie eating contest knowing that the town is going to sacrifice archie later that night. nothing about this is hard to understand