How to use CCBitmapFontAtlas in iPhone cocos2D?

CCBitmapFontAtlas faster than CCLabel.
Labels that update fast at the expense of more memory usage, like any other CCSprite,is the specialty of the CCBitmapFontAtlas class

//Usage...
CCBitmapFontAtlas scoreLabel = [CCBitmapFontAtlas bitmapFontAtlasWithString:@"0"
fntFile:@"bitmapfont.fnt"];