LED lights on the network adapter indicate network connectivity. Two types of LED are used, connectivity LED for network speed (like solid yellow means for 10Mbps; solid green for 100Mbps or 1000Mbps.) but if it is blinking, then intermittent problem. and the activity LED blinks when data passes.
OS also shows network connectivity status in system tray on data passing, no connection or new connection established. as two monitors diagonally, one on top of the other. Right-click them and select Status, to see the status of the adapter.