A king in the UK today is not in charge of the laws. He doesn't decide things like school holidays or tax. The Prime Minister and the people elected to Parliament do that. The King's job is more about representing the country, hosting visitors from other places, and supporting hundreds of charities.
Charles III is also King of 14 other countries, including Canada, Australia and New Zealand. He doesn't live in those countries, but he is still their official head of state. Together these countries are called the 'Commonwealth realms'.
He is famous for caring about the natural world. He started farming organically on his own land back in the 1980s, when not many people had heard the word. He also looks after old buildings, helps train young people through a charity called the Prince's Trust (now the King's Trust), and is keen on the arts.
The official home of the King is Buckingham Palace in London. It has 775 rooms and a special guard of soldiers in red coats and tall bear-fur hats. The famous 'Changing of the Guard' ceremony outside the palace is watched by thousands of visitors every year.