Basically, Andy Burnham has majority support within the Labour Party to be the next PM, but he wasn’t a member of Parliament, which is necessary to challenge a current PM for the role. So the Parliament member for Makerfield resigned to hold a special election so that he could (hopefully) win the seat, which he did, and now he’s set to become the new PM.
John Oliver did an episode of Last Week Tonight on it recently. https://www.youtube.com/watch?v=RZL_TctrNco
Basically, Andy Burnham has majority support within the Labour Party to be the next PM, but he wasn’t a member of Parliament, which is necessary to challenge a current PM for the role. So the Parliament member for Makerfield resigned to hold a special election so that he could (hopefully) win the seat, which he did, and now he’s set to become the new PM.