How to use the Achievements module? I want to create some kind of challenges for users. And when it is fulfilled the user is able to unlock a new level and gain some kind of victory say in terms of a new theme, i.e, after completion of that challenge the user is awarded a new theme which the user can set as their theme.

I want to do this using the Achievements module. However there seems to be almost no documentation available, so I'm looking for ideas on how to proceed.

Note: I have basic understanding of php and have created few basic modules as described in drupal.org.
The comments and example code in the documentation: achievements.api.php show how to create a new achievement.

There is no administration interface, you must create a module and use the hooks described in the above link to create new achievements.