Back to school - again

My son has just come home for a couple of days. He is at Stafford University, in his final year studying Automotive Engineering. He has brought with him some books about "Vibrations". I have looked at some of this stuff and got about as far as 1st grade, here it is:



That's about as far I can get. He wants to move on the Lagrage theory, but I just can't get it...