Procedural due process - The rules. People in charge have to follow them. There are procedures for managing situations when a person is accused of misconduct. Example: A student is accused of cheating. Procedural due process is what they do to prove that, and how they decide to punish him.
Substantive due process - The rules don't apply, or they're ridiculous. Standard procedures for managing situations don't always work. Example: A student is accused of cheating. Substantive due process addresses whether the rules are valid, make sense, and work.