Procedural law consists of the set of rules that govern the proceedings of the court in criminal lawsuits as well as civil and administrative proceedings. The court needs to conform to the standards setup by procedural law, while during the proceedings. These rules ensure fair practice and consistency in the "due process".
Substantive law is a statutory law that deals with the legal relationship between people or the people and the state. Therefore, substantive law defines the rights and duties of the people, but procedural law lays down the rules with the help of which they are enforced. The differences between the two need to be studied in greater detail, for better understanding.
Differences in Structure and Content
In order to understand the differences between the structure and content of substantative and procedural law, let's use an example. If a person is accused and undergoing a trial, substantive law prescribes the punishment that the under-trial will face if convicted. Substantative law also defines the types of crimes and the severity depending upon factors such as whether the person is a repeat offender, whether it is a hate crime, whether it was self-defense etc. It also defines the responsibilities and rights of the accused.
Procedural law, on the other hand, provides the state with the machinery to enforce the substantive laws on the people. Procedural law comprises the rules by which a court hears and determines what happens in civil or criminal proceedings. Procedural law deals with the method and means by which substantive law is made and administered. In other words, substantive law deals with the substance of the case, how the charges are to be handled and how the facts are to be dealt with; while procedural law will give a step by step action plan on how the case is supposed to proceed in order to achieve the desired goals. Therefore its procedural law that helps decide whether the case requires trial or otherwise.
Here's another good video discussing substance vs. procedure by Prof. Ian Ayers, Yale Law School.
Powers of Substantive vs. Procedural Laws
Substantive law is an independent set of laws that decide the fate of a case. It can actually decide the fate of the under-trial, whether he wins or loses and even the compensation amounts etc. Procedural laws on the other hand, have no independent existence. Therefore, procedural laws only tell us how the legal process is to be executed, whereas substantive laws have the power to offer legal solution.
Differences in Application
Another important difference lies in the applications of the two. Procedural laws are applicable in non legal contexts, whereas substantive laws are not. So, basically the essential substance of a trial is underlined by substantive law, whereas procedural law chalks out the steps to get there.
An example of substantive law is how degrees of murder are defined. Depending upon the circumstances and whether the muderer had the intent to commit the crime, the same act of homicide can fall under different levels of punishment. This is defined in the statute and is substantive law.
Examples of procedural laws include the time allowed for one party to sue another and the rules governing the process of the lawsuit.