The LEDs namely L, TX and RX on the board. Furthermore, whenever the board is connected, the L LED blinks to the frequency of the delay that I set. [Eg: delay(1000);] If I miss any other LED, do mention their purposes as well! Thank you
'L' shows the state of pin13 which is programmable by you for any purpose, whether to read or write to an external device, or just for turn the LED on and off as you have done.
'RX' and 'TX' show the states of the Receive and Transmit pins, respectively, and allow you see when serial communication is taking place.