The LED-light is located next to the USB-C input port. It is there to tell you the current state of your tracker.

When charger is plugged in
Red - Less than 90% battery level.
Green - More than or equal to 90% battery level.

When charger is not plugged in
Blue - Tracker is searching for GPS signal

Green - Tracker is connecting to the internet and about to send an update, with or without a GPS position.