They're called nav/com radios (not computers although they do have a lot of PCB's etc in their construction)
In an aircraft with two nav/com units, the active com-1 frequency is the one both you and your passenger/co-pilot will be monitoring. Hopefully, you will have entered the standby frequency (i.e your next controller to call) on com-2. When you want to make the standby frequency the active frequency you advise the controller on the first active frequency that you are changing to 123.xxx, say, and then press the toggle key to make com-2 the active. The audio panel will sort out the electronics switching, but in any case, on most audio panels the active will cut in when a controller speaks even if you are monitoring audio on the standby com-2.