An individual person who has been harmed by a product or company can bring a class action suit on behalf of others who have been injured in the same manner. A class action lawsuit typically starts with a single person who has been injured. Once the class action has been started, it is common for other people to join the suit.
Generally, the court certifies a class action lawsuit because there are too many people to make individual lawsuits practical. Most of the time hundreds or thousands of people are involved in class action lawsuits.
Some class action statutes have a minimum number of class members that are required by law in order to be certified as a class action suit. However, most of the time a civil court certifies a case as class action because there are too many people to be named as parties in the lawsuit.
If a class member does not want to participate in the class action suit, he or she can hire their own lawyer to pursue an individual case.