There are two very different things one might want to do with Augeas:
- use its public API and existing file format descriptions to edit config files
- write new file format descriptions
Using the Augeas API
If you are mainly interested in Augeas' public API, the best documentation right now is the public header file augeas.h and augtool's help command. The commands in augtool mirror the public API closely, and therefore give you an easy way to tinker with it without writing any code.
If you are mainly interested in describing new file formats, you should read about lenses, the basic building blocks of the transformation between files and the tree, and the tutorial on writing schemas.