Good question. In The Crucible, Tituba's role and significance is often overlooked. Like many others accused of witchcraft, she is both innocent and guilty, but because of the social circumstances, I would say she's more innocent than guilty. Tituba is Reverend Parris' slave. She is from Barbados which conjures up images of the practice of Voodoo, although in Barbados the historical practice has been called Obeah, a folk magic mysticism similar to Voodoo. This doesn't help her case in the eyes of Salem's religious fanatics.
I would argue that Titbua, being a slave, was just trying to make friends, to appease the girls that night in the woods by "freeing their spirits" so to speak. It's clear that the girls, including Tituba, were doing this in fun. They lost their minds when they got caught because they know how strictly religious Salem is. Betty and particularly Abby are the ones who really throw fuel onto the fire of hysteria. Tituba was just a pawn in their game. In Act 1, Abby says Tituba offered her blood to drink and she refused. Right after that, Abby says Tituba made her and Betty drink. Throughout the course of the play, Abby looks for others to blame and this time it was Tituba. In fact, it was Abby who asked Titbua to do all these things, to help get her and the other girls into the spirit of their playing at magic in the woods.
Tituba does accuse Sarah Good and Goody Osburn, but she is pressured into doing so. This is after Abby falsely charges Tituba with sending her spirit on her. Tituba, fearing for her own life, concludes that something must be 'witchin' the girls, so Tituba is even pressured into claiming that the Devil was involved when she witnessed no such thing.
Tituba is not blameless in all of this. But because she was a slave, she was already in a subservient position and therefore she had more to fear, so her accusations cannot be condoned but they are at least understandable. Had Tituba been Parris' white daughter rather than his black slave, I imagine she would not have been scapegoated this way.