From a practical perspective anyone with the login can see a plot of where the aircraft has been at regular intervals overlayed on google maps. If you have multiple aircraft it can plot all or some of the different aircraft in your fleet.
Basically
Aircraft power applied - spidertracks warms up, gets gps position and sends first position report to their server
Takeoff - either by the pilot pressing a button or automatically once the device detects a G/S over a specified limit it sends position report to the server and identifies that the aircraft is airborne
At regular intervals, say 10 mins apart it sends the GPS lat / long, time, g/s, heading and altitude info the the server
Landing - either by the pilot pressing a button or automatically once the device detects a G/S below a specified limit it sends a position report to the server and identifies the aircraft has landed.
It also has emergency modes that can be selected by the pilot that starts sending position reports at a much shorter interval (ie 1 min or something like that) as well as sending a warning message to the server which then will send an sms and/or e-mail to person/s specified by you that the pilot has activated the emergency mode of the system.
There is also an urgency mode that is similar to the emergency mode.
All of this info is logged on the server permanently and can be reviewed at a later date - it doesn't automatically get deleted.
Also there is an iphone app which allows a user with the login credentials to see which aircraft have an active unit and the movements of the current flight.
The spot messenger works in a similar way, however it really is oriented towards individual users and not in a flying situation. It is however much cheaper and IMO worth it if you do long distance remote driving outside of mobile phone coverage (at ground level that is pretty much all of the GAFA).