It is to protect people from being sued by others when they are trying to help. I think it came about when someone sued a bystander for doing CPR on them (saving them) but breaking their ribs in the process (which is actually the proper way to do CPR). But after this people were hesistant to do good deeds and the law was put in place to protect people who are helping in good faith. but this does not protect you if you do something out of your scope of training.

its just like anywhere else. If you see anything wrong then report it or if you can try to take action yourself

Good Samaritan laws are laws or acts protecting those who choose to serve and tend to others who are injured or ill. They are intended to reduce bystanders' hesitation to assist, for fear of being sued or prosecuted for unintentional injury or wrongful death