The first one lights up when Num Lock is pressed, the second one springs into action when Caps Lock is pressed (even when it is accidentally pressed, reminds me of someone who "trained" his assistant to not accidentally go into caps by blu tacking an upside down (sharp side up!) drawing pin onto the caps lock key) but I can't work out what makes the third one light up?
I think it depends on you computer. I have no such buttons on mine. RFM as in Read the F*****G (flipping) Manual. you can usually download these. I had to download one for my new mobile phone as I had not clue how to use it.