What does the news of what is happening in Andover have to do with the Salem Witch Trials?
In Andover, the people were rebelling against witchcraft. They began to throw witchcraft cases out of the court.
The reason this is important has to do with Abigail's fears. Abigail and the girls' testimony would come into question and the charges would be founded on nothing for all of the people they have convicted of witchcraft. These cases would have to be thrown out and the people freed from jails. Restitution would need to be paid. Danforth would not accept what had happened in Andover as fact.
This understanding actually sparked Abby's fleeing. She left knowing that she would have to reconcile what had occured in Salem. Her gig was up, her lies would be exposed. This likely also gave the Salemites a foothold to try to discuss the cases further with Danforth. However, he wanted to keep going.
It has to do with what is happening in Salem because it worries Parris.
Parris has heard that the people in Andover have stopped believing in witchcraft, or at least that they no longer believe in their court that is conducting witch trials. He worries that this sort of idea will spread to Salem and people in Salem will turn against the trials.
This worries him because he has been a big part of having the trials held. He worries that people will turn against him too. He has, throughout this play, been really concerned with his image and his place in the society. Now he feels that this is threatened by what is going on in Andover and the possibility of it spreading to Salem.
In Andover, popular and well-respected people were accused first. Hence,the people in Andover had doubts in the accusations and they turned the blame back to the accusers. Seeing what had happened in Andover, Abigail knew that she would be questioned about her doings, such as accusing people of witchcraft in salem, and so her lies would be exposed. Therefore, she escaped with Mercy Lewis to somewhere which was not stated in the story.