First of all to test this out you need to build ChucK from source. You can get the source like so:
$ svn checkout https://chuck-dev.stanford.edu/svn/chuck/trunk/src chuck
And then build:
$ cd chuck $ make [osx | linux-jack | linux-alsa | win32]
(selecting your platform from one of those options)
So basically, there is a test chugin called "Bitcrusher" that I wrote as an example of how to write a chugin. You can use this as the starting point for new chugins.
$ cd test/dl/Bitcrusher $ make -f makefile.linux $ sudo make -f makefile.linux install $ ../../../chuck Bitcrusher-test.ck
makefile.win32 as necessary)
You should hear a delayed version of the adc/mic input thats been decimated and artificially quantized to a low bitrate sample-format. You can use this as a framework to write any new chugins you are interested in. Right now we don't envision this being used for stuff other than new ugens, as theres a whole lot more work involved to make a useful framework for general purpose libraries.