Check out the whole large-scale documentation of roboyVR here: http://roboyvr-experience.readthedocs.io/en/develop/
How it works:
Roboy and its behavior is simulated on the virtual machine via ROS. Important information
regarding roboy's movement are then sent through a ROSbridge(e.g. messages) towards Unity.
In Unity roboy is rendered and constantly updated concerning positions, rotations, etc.
With the help of a VR-Headset you can watch roboy move around in a virtual space.
Follow the installation instructions in the documentation