There are a number of great resources available around Houdini that have helped me and likely can help you as you explore Houdini. Smashing Magazine has a great Houdini article (unfortunately a little outdated now) that'll give you a good high-level overview. I've also given a talk, Magic Tricks with Houdini, the latest version is embedded, if videos are more your speed
If you're looking for more demos, @iamvdo has some truly fantastic stuff over on his website css-houdini.rocks. The Google Chrome Labs team also has a great set of demos with source you can play with. I've personally learned most by tweaking the samples here.
Because everyone loves reading the raw specs, and there are lots of them for Houdini, you can find them below:
Finally, there are people. Tab Atkins is the one responsible for first getting me interested in Houdini and they have their name plastered all over the specs. Surma has been an invaluable resource answering all of my Houdini questions. Surma fingers are all over the Google Chrome Labs demos. Finally, there's Ian Kilpatrick whose actually implementing this stuff in Blink! Ian built the Masonry Layout API demo!
And of course, I'm always happy to chat! @snugug on Twitter, the Internet, and in general.