Four flats at beginning of sheet music?

I currently want to learn this song on piano, and I have the sheet music. I can read music fairly well since music was a subject to be taught from Kinder- Year 8, but we never learnt what to do when there are flats or sharps after the treble clef at the beginning of the song. In my sheet music here there are 4 flats for both the treble and bass clef sections. I'm not sure what the proper name for teh 4 flats is obviously. What will this do to the notes? If you could give me a site or something that explains it well, or if you are happy enough to give up some of your time to explain it here, that woudl be great. Thanks