That's a huge subject! The short version is that Henry VIII wanted to divorce Catherine of Aragon, the pope wouldn't let him as the catholic church does not recognise divorce, so he declared himself head of the church in England and the pope excommunicated him. The Archbishop of Canterbury, Thomas Cranmer, then gave him what he wanted. However, Henry wanted nothing else to change in the church and the Church of England remained very catholic until he died 14 years later, at which point Cranmer was able to turn the (now independent) English church into a protestant one.
Henry's son, Edward VI, was very young and that left the country in the hands of protestant nobles. He died only a few years later and was succeeded by his sister Mary, who was very catholic. Under her many prominent churchmen, including Cranmer, were executed. She died only a few years after that and was succeeded by Elizabeth I, who was protestant. The catholic church remained illegal in England for another few centuries after that.
Essentially the significance of Henry is that he broke away from Rome and that allowed Cranmer, later on, to completely change what the church in England was like.
If you google Henry VIII and Thomas Cranmer you will no doubt find a LOT more.