The Charm Tools PPA includes the
charms-tools package, which is useful for creating and testing charms.
charm create <ubuntu-package-name> will create a basic charm with filled metadata for you. Use this if you want to build a charm out of something that is already packaged in Ubuntu.
charm create whatever will just create a blank charm for you to edit if you want to create a charm for something else, for example one that pulls from the latest upstream source or for something that is not available as a package in Ubuntu.
And lastly you'll want
charm proof to test to see if your charm is correct.