Finn wants to help Puck to graduate. they use famous songs to learn geography. Here he is trying to learn about Spain with the famous song in My Fair Lady or Pygmalion
"the rain in Spain stays mainly on the plain"
( it was used in My fair lady to teach her to pronounce the P sound well)
click on
https://www.youtube.com/watch?v=uVmU3iANbgk