The Conbee2 is a small USB stick with a ZigBee radio inside that can have devices paired with it in much the same was as your HE hub, but it accommodates a few peculiarities in how IKEA chose to implement the ZigBee protocol that Hubitat does not. This USB stick plugs into my raspberry pi, including an extension cable, and I have installed the recommended deConz software also on the raspberry pi.
Deconz has an API meaning we can write code to communicate with deConz from the HE hub, which one Community member has done here:
You don't have to use a raspberry pi, you can run the conbee2 and deConz on Windows I believe, but I don't have any experience with that setup or know whether the community driver works with that setup.
With all that installed, the driver detects each device connected to the conbee2 stick and creates virtual devices representing those on HE. When you press the on button on a remote, it tells deConz, which then tells HE, and you then setup rules / automations that are triggered by the virtual device representing that remote.
Make sense.... 
