The United Kingdom (including England) is a constitutional monarchy. The monarch (currently King Charles III) serves as head of state without real political power. Actual governing is done by the elected Prime Minister and Parliament.
Determined by the Act of Settlement 1701: throne passes to the closest Protestant descendant of Sophia, Electress of Hanover (granddaughter of James I/VI). Her descendants have ruled since.
When a monarch dies, their eldest child automatically succeeds. If no children, the next Protestant in line inherits.
Largely symbolic: representing UK abroad, head of armed forces, granting royal assent to legislation, meeting with PM. No lawmaking or political interference power.
The monarchy remains popular, though debate exists about its future (republic vs. monarchy).