Most Ethernet ports will have two LED's, one on the left side and one on the right side.
One will indicate connection state (Solid) and the other connection activity (Flashing).
Different devices or hardware manufactures may have these on either side
This indicates the speed the device is running at.
Amber = 1000Mbps.
Green = 100Mbps
No LED = 10Mbps
You'll notice in this last image that the LED on the other side is on, which brings us to below
This is used to indicate link activity.
This will simply flash whenever there is network activity, and will only be the one colour.