Why does King Charles have a coronation ceremony and what happens?

(This April 18 story has been corrected to change years to 350 in the penultimate paragraph) LONDON (Reuters) - King Charles became monarch of the United Kingdom and 14 other realms on the death of his mother Queen Elizabeth in September, but in May he will be crowned in a ceremony full of pomp, pageantry and solemn religious significance. Why is he crowned and what does it all mean? WHAT'S THE HISTORY OF CORONATIONS? For the best part of a thousand years, the kings and queens of England and Britain have been crowned at London's Westminster Abbey in a ceremony that has changed little throughou...