One of the songs they always played was "Sympathy for the Devil' by the Rolling Stones. Now, if you listen to the Stones version there is a lot of things going on in the song. Musicans refer to it as muti-tracking, the process of having recording a lot of parts to a song. You record a piece at a time so you don't have to record 20 things all at the same time. In fact a lot of songs have the main vocals muti-tracked to strengthen them.
There is one neat thing going on in "Sympathy." The background vocals thoughout the song goes, "Woo, woo! Woo woo!" It's strange because it's like four minutes of singing, "Woo, woo!" The next time you listen to it on the radio try singing along with the background vocals instead of the main vocals. It starts to get really tiring. I almost felt sorry for the guys in my friends band who sung backup on that song.
So it's something to think about. Really the next time it comes on the radio, sing backup. You will really start to get tired of doing so. Everyone wishes they were Mick Jagger.