The ComBridge can be used to link a value from one device to another. For example, let's say you want a Modbus device's value to go into a SLC500 which cannot communicate Modbus. In AdvancedHMI, you would add a driver for the Modbus device and one for the SLC500. Then add a ComBridge to point to the Modbus driver as a source and the SLC driver as the target, then set the addresses to link.
The Checkbox is really not much more than an illuminated button. The check is tied to a bit and when it is clicked, it will toggle the bit.