The constitutional monarchy of the United Kingdom is the form of government for the United Kingdom, the crown dependencies of Guernsey, Jersey and the Isle of Man, the British Overseas Territories, and the 14 other Commonwealth realms, including Australia, Canada, and New Zealand.
King Charles III will be crowned on 6 May 2023 in London. Many events are expected in the UK in the weeks leading up to the coronation, and especially on the day. Smaller celebrations will occur in the Commonwealth realms.
The monarchy was consolidated in Medieval England. In 1603, it unified with Scotland to form the Kingdom of Great Britain (which was followed by a union of states in 1707), and with Ireland in 1801 to form the United Kingdom. Britain came to rule the British Empire, and the monarch is still the Head of State for the Commonwealth realms. In these countries, the monarch is represented by a governor general, who performs the monarch's duties in his absence. While the governors-general used to be sent from Britain during the height of the British Empire, in modern times the governor-general is almost always from the country they are representing the monarch in. The British monarch also holds the title of "Head of the Commonwealth".
The Commonwealth of Nations, formerly known as the British Commonwealth, is an international organisation which mostly consists of former British colonies. Today most of them have no formal association with the monarchy (apart from symbolically recognising him as "Head of the Commonwealth"), with most members being republics (Pakistan, India, South Africa, etc.), while Malaysia, Brunei, Eswatini, Lesotho and Tonga have their own indigenous monarchs. Four Commonwealth members were never part of the British Empire: Gabon, Mozambique, Rwanda, and Togo.
These days, the British monarch is largely regarded as a ceremonial figurehead, with the prime minister wielding the most authority in government. However, the monarch still legally has the right to veto bills (prospective laws) that have been passed by Parliament, though this right has not been exercised since Queen Anne did so in 1708. The monarch also regularly meets with the prime minister, which may give him some influence over British politics, and all ambassadorial appointments have to be approved by the monarch.
Most years, and certainly after a general election, the monarch leads the State Opening of Parliament, during which he delivers the Speech from the Throne to both houses of Parliament on behalf of the government, more popularly known as the King's Speech. This ceremony is steeped in tradition and is a visual spectacle, one of the few times when all branches of the British government gather in a single place. During the session, you can see the Lords and the Speaker of the House of Commons, as well as various other crown office holders, don their ceremonial robes. Several traditions date back to a time when the relationship between the monarch and Parliament was much more fraught. For instance, the monarch has been barred from entering the House of Commons chamber since the English Civil War, and must instead send a representative (ominously called Black Rod) to summon the Members of Parliament (MPs) for the Opening. Traditionally, MPs slam the door of the Commons in the face of Black Rod, just as they did to Charles I in 1642. Black Rod then raps the door three times with her rod, and the MPs file out led by the Speaker and the Serjeant at Arms, following her to the House of Lords chamber where the King delivers his speech. One MP is also always held as a "hostage MP" at Buckingham Palace prior to the monarch's departure, ostensibly to guarantee his safe return. While attendance at the Palace of Westminster is limited to special guests, the monarch's procession from Buckingham Palace to the Palace of Westminster may be viewed from the roadside by the general public, and the entire proceeding is broadcast live by the BBC.
The residences of the Royal Family give limited or no access to the public.
The main set of Crown Jewels can be seen in the Tower of London, and a smaller collection, the Honours of Scotland, can be seen in Edinburgh Castle. The Jewels are removed from display when they are required for royal use.
The British monarch is also the head of state of 14 other Commonwealth countries, known as the Commonwealth realms:
In each of these countries, the King has an official residence where he stays when visiting those countries. When he is not around, that residence serves as the official residence of the governor general.
The highly-trained King's Guard are used to dealing with tourists, and are famed for their stoicism in the face of almost anything. Indeed, they may look somewhat quaint in their ceremonial uniforms. However, they are emphatically not purely symbolic figures stationed as a curiosity for tourists; they are real, serving soldiers with live weapons whose job is to defend the Royal Family. Touching the guards, getting too close, or standing in their way when they are marching will get you bellowed at with their bayonets pointed at you, as some tourists have learnt the hard way (with numerous videos on YouTube to prove it). In the latter case, you will be simply shoved away as the guard proceeds on his march on the originally-intended path. The guards are authorised to use deadly force if they believe that the King's life is in danger.