Global Listening allows BlueConic to pick up general visitor information. It picks up technical information like the browser name or the device, but also general statistical information like the number of visits or the average time of a visit. See "what kind of information does BlueConic collect?" for details on profile properties populated by the global listener.
Installing the Global Listener plugin is enough to activate it on all channels. No additional configuration is required. Note that even though the Global Listener will not be listed under "Profiles > Listeners", it will still be active.
The Global Listener is a standard plugin.