First aid is complex and situation specific, so the more informed and better trained you are the more prepared you are to deal with any unexpected illness or injury. When someone suffers an injury or sudden illness, first aid is your initial course of action.
But first aid is more than having a properly stocked first-aid kid; it is being able to prevent, prepare for, recognize, and easily take care of small accidents, and knowing what to do in the case of an emergency. You can treat most common illnesses and injuries when you know what to do, but first you must decide if first aid will be adequate or if you need professional help. And when the condition warrants measures beyond first aid, knowing how to act until help arrives can save someone's life.