Install it first:

gem install pdd

Run it locally and read its output:

pdd --help

Every puzzle has to be formatted like this:

/**
 * @todo #234:15m/DEV This is something to do later
 *  in one of the next releases
 */

It starts with @todo, followed by a space and a puzzle marker. Possible formats of puzzle markers:

#224
#TEST-13
#55:45min
#67/DES
#678:40m/DEV

Read this article about Puzzle Drive Development.