The sentence is an example of a cause and effect reasoning. It helps to stablish the relationship between an event that comes first, and the one that takes place after the former. This type of reasoning provides the necessary information and details to understand why certain events happens as they do.
Answer:
The Order is a group of wizards, led by Hogwarts headmaster Albus Dumbledore, dedicated to fighting evil Lord Voldemort and his followers. ... Harry used magic to fight off the dementors, and since underage wizards are not permitted to use their wands outside of school, he must face a disciplinary hearing at the Ministry.
That is the summary of the, book you should pick what you like and turn it into one sentence.
