If you haven’t previously documented the device id’s of the Insteon devices, you’ll need to get the device id off of the device so you know where it’s located and maybe the device type. If you don’t have many devices and don’t know it’s device ID, you can configure one with a device type and then see which one is controlled after it’s set up in openHAB.
Before jumping in and trying to set up the insteon binding, my recommendation is to first understand how openHab works.