The basic idea of pydoctor is that it examines source code and produces html that describes that source code. It does this using a command line tool which has a rather large number of options (although once you've worked out which ones you want you can put them in a config file).
The simplest invocation is something like "pydoctor --add-package=/path/to/a/package --make-html". This will (hopefully) produce html in a directory called "apidocs".
To learn more, read the output of "pydoctor --help" and look at the example *.cfg files that are checked in to pydoctor svn. Or read the source. Or wait for me to write more of this web page. Or write it for me :-)