"Shiawase nara te o tatakou (If You're Happy, Clap Your Hands)" is a popular Japanese song that is based on a Spanish folk song. It became a big hit in 1964, when the song was released by Kyuu Sakamoto. As 1964 was the year that Tokyo hosted the Olympics, the song was heard and loved by many foreign visitors and athletes. As a result it became known all over the world.
The "nara" used in the song, indicates a supposition and result.
Learn more about the song and read its lyrics and learn more about nara in this article: http://japanese.about.com/od/grammarlessons/a/Conditional-Nara-And-The-Song-Shiawase-Nara-Te-O-Tatakou.htm?nl=1