Adding a song into a presentation

I am creating a presentation for my English class and I was trying to add a song into my whole presentation but it only works for one slide or until I click my mouse. Can anybody help me keep the song playing through the whole presentation?

Sorry, you can find the answer in the FAQ but, at the moment, only in French:

If you don’t read French try this: Google Traduction

Quick translation: To play sound throughout the presentation, go to the slide where the sound should start, add the sound as a transition sound, and have it play. The transition sound will play continuously (limitation: starting another sound will stop the transition sound)