Backing up Calibre libraries - help please.

A search for how to backup files on this site or in Calibre "Help" leaves one in limbo. It seems like such a basic and necessary step that should be included in the initial steps for using Calibre, but I'm stumped.

When I click the Calibre icon/library maintenance/library metadata backup status, there is an option to queue all books for backup. I thought this was the start of the backup process but it doesn't do anything beyond that.

Since I did not discover a backup process through Calibre, I have copied my libraries to an external hard drive but am wondering how to avoid a complete backup each time and only backup items that have changed or are new.

Can someone recommend simple software that would do this?

Thank you!