The blender to lua exporter generates a pair of files, a LUA fragment with the extension '.b2l' and a binary file with the extension '.b2l.bin'. The LUA file describes the blend's scene graph along with meta data neccisary to intepret the binary file. The binary file stores arrays of numerical data such as vertex data, object, and bone transforms. The byte offsets of these arrays are stored in the LUA tables for easy location. This allows the output to be efficiently processed from C/C++ code as well as eliminates rounding errors inherent to text to binary conversions.
The exact format of the files is described in a comment section at the top of the export script. In most cases fields exported in the LUA data have a 1-1 mapping to the representation in the Blender Python API. Field's that are either not well documented or poorly suited for real-time rendering are ommitted.
Since material data is generally not very portable across different renderers the B2L format omits material details and only stores the material names and which submeshes they apply to. To render your models you will need to reconstruct the material data in a form suitable for your renderer.
Bone and object transforms are stored for every frame for objects that are animated. Raw function curves and action data is not stored yet but it may be added if it can be documented properly. Basic NLA track and strip data are stored to make it easy for external tools to assocated animation frames with specific actions.