The library is a mess of parts right now with some unit tests that show how it works.
All inbound traffic packed into messages and routed to inbound handlers. You can add your own or you can poll the ones that exist.
Outbound traffic can be sent directly via the API or through a message based API. I intend that the Message API is the future of the library once resource management has been added.
Look at the Integration tests to play with it. They expect at least one IOIO V5xx on a COM port with pins 31 and 32 tied together.