B2U Reference and Documentation
Step 1 - Unity Importer:
Make sure the B2U unitypackage was imported at your unity project. The final path would like "Assets/B2U/"
Step 2 - Blender Exporter:
Go to File/User Preferences/Add-ons and Click in "Install Add-on From File"
Set the path to the "b2uexporter.zip" file that is inside the "Assets/B2U" folder, install and set it active in blender.