In The Crucible, acts 1, 2, and 3 all end by clearly showing how Abigail is firmly in control of events. She is clearly manipulating people.
Act 1 ends with Abigail crying out the names of various "witches," and she is praised for it. Act 2 ends, and audiences see just how powerful she has become. Abigail successfully figured out how to get Elizabeth Proctor arrested and likely out of the way so she can pursue John. In the end of Act 2, we also see that the other girls, like Mary Warren, fear Abigail and how she might turn on them. Abigail will do this to Mary Warren at the end of act 3, and that causes Mary Warren to accuse John. Keep in mind that Abigail retains that power despite being announced as a "whore."
The three acts are different in how they portray Hale. Act 1 shows Hale firm in his convictions about witchcraft. He believes he has found the source of evil, and he has full confidence that he and the court will rid Salem of witchcraft. Act 2 shows Hale less confident in the truth and facts of the supposed witchcraft. He is clearly beginning to question the authenticity of events and accusations. By the end of act 3, Hale denounces the proceedings and quits the court.