Originally, Abigail claimed to her uncle, Reverend Parris, that the girls were just dancing, and she tells him that there was "nothin' more. I swear it, uncle." When Parris mentions that he thought he saw someone running around naked, she acts shocked and denies it, saying, "No one was naked! You mistake yourself, uncle!" So, that's the word on the street up until Hale comes. She even admits to John Proctor that "we were dancin' in the woods last night" and that was all. But then, Hale shows up, and all of a sudden witchcraft is an accusation that is floating around. Hale is more specific in his questioning. Parris himself confesses more than we knew he had seen. He says, "I saw a kettle in the grass," implying they were making soup, and "there were something movement-in the soup." So, Parris admits having seen soup with something moving in it. So, Abby has to defend herself against that, and she says, "That jumped in, we never put it in!" referring to a frog that just happened to jump into their pot. She continues by saying that it was Tituba who was conjuring spirits; she figures if she can pass it off on Tituba, she'll be safe. Then, when Tituba "confesses" and starts shouting out names of witches, Hale starts treating her like an angel sent to cleanse Salem of evil, so Abby thinks this could be her way out. She too "confesses" that she saw the devil and starts naming names; she does so in order to get the blame taken off of her, and to get out of trouble.
So, Hale discovers that there was a kettle with a frog in it, and that Tituba was actually conjuring spirits. But what he still doesn't know, is what we learn when Abby is talking to the girls when they are alone: Abby drank a magic charm of chicken blood, to cast a spell that would kill Elizabeth Proctor, and she begged Tituba to show her how to cast that spell. That is the real truth that gets covered up in all of this, and no one ever finds that out.