Complex sentence: The GSOC is mandated to provide an independent and effective civilian oversight of policing and to deal with the public's complaints concerning Gardaí fairly and efficiently so that everyone can have confidence in the complaints system.
Split into simpler sentences: The GSOC is to provide an independent and effective civilian oversight of policing. It is to deal with the public's complaints concerning Gardaí fairly and efficiently so that everyone can have confidence in the complaints system.