The Power of the King
England was ruled by Norman kings for about 150 years starting with William the Conqueror in 1066. Unfortunately, King Stephen ended the line by being a very weak king. England was almost destroyed by the constant raids by the Scots and the Welsh. Eventually the original successor to the Crown, Countess Matilda (she was not well supported because she was a woman), overthrew his wimpy butt and put her son, Henry of Anjou on the throne.
Henry II's fourth child, John Lackland, became King of England in 1199 after the Crusader-King Richard the Lionhart died without any children. Richard was an absent but popular King. John...not so much. He was fat, cruel, self-indulgent, selfish and avaricious. Historically, he's been called "the worst English King". The raising of punitive taxes and constantly pissing off the Pope will eventually unite all elements of society, clerical and lay, against him. That has not happened...quite yet. Powerful Barons and military strength keep the grumblings at bay. At least, grumblings in public.
Money makes the Kingdom go 'round. The major ways the King collects money is in bi-monthly taxes and fines for wrongdoing. You'll want to familiarize yourself with the The King's Laws. Your character claiming ignorance of the law will not save them from being fined.