Substantive law is a body of law that defines the rights, duties, and obligations of people. Substantive law provides rights to people. Procedural law is a body of law that deals with the procedure when the substantive law is violated. Procedural law describes what will happen when substantive rights are violated. When substantive law is breached then procedural law begins. It's means when the rights of any person violated then procedural law takes place.
Constitution and law have provided many rights as fundamental rights and legal rights to citizens. But there is no meaning of such rights if remedies are not provided to it. For example, if a person's right to freedom is violated then he can go to court for remedies.
But what will happen if there is no provision for such a process. Sure there will be jungle rule and those who remain strong, can do as they like and disturb others' rights. So there must be procedural law to provide remedies to the victim and punishment to bad people.
Law has defined many criminal activities but what will happen if the law does not mention punishment for those who conduct such criminal offenses. Crime like rape, theft, murder, and many more crimes will be increased day by day. In the lack of procedural law or remedies, the victims cannot get justice and criminals move freely and commit crimes again and again.
So, procedural law is necessary to provide justice to the people and stop people from committing crimes and breaching of law.