First, if you haven't done so already, check out the main usage[http://ts.freelancing-gods.com/usage.html] page. Once you've done that, the next place to look for information is the specific method docs - ThinkingSphinx::Search and ThinkingSphinx::Index::Builder in particular.
Keep in mind that while Thinking Sphinx works for ActiveRecord with Merb, it doesn't yet support DataMapper (although that is planned).
Fork on GitHub and after you've committed tested patches, send a pull request.
To get the spec suite running, you will need to install the not-a-mock gem if you don't already have it:
You should now have a passing test suite from which to build your patch on.
Since I first released this library, there's been quite a few people who have submitted patches, to my immense gratitude. Others have suggested syntax changes and general improvements. So my thanks to the following people: