Returns the header hash (32-bytes) of a block at the given height in the selected chain.

How is this used?

You're in a library full of books arranged in a precise order. You're looking for a book at a specific position on the shelf but only have the book's placement number, not its title. The 'getblockhash' command in the Bitcoin blockchain works in a similar way. By providing the height (or position) of a block in the blockchain (the shelf), this command returns the block's hash (like the unique title of the book), allowing you to identify and then access the block's detailed information.