Learn through the Examples. Most of the Heron widgets and data components have simple examples that demonstrate their use. By looking through the examples’ sources for the examples, you can learn how to build a Heron application. You may even take an example as a starting point.
The API Reference covers details on developing with Heron. Generated from the comments in the code.
Documentation for end-users (of Heron applications) is in progress. As a start we have a Heron End-User Manual (PDF Dutch).