In principle what is meant by substantive law is the law that defines the legal rights of parties vis-a-vis one another or with respect to the state. Thus in a lawsuit contracts, property law, torts, civil rights, employment law, etc. would normally be regarded as substantive. By contrast “procedural law” refers to the rules that govern how a case is tried before the courts or tribunals of a jurisdiciton (or what arbitration law applies.)
In practice the distinction is messy – there are many issues of procedural law, such as rules of evidence, burden of proof, discovery, pre-judgement interest, injunctive relief, etc. that have a very substantive impact on litigation. Moreover, different jurisdictions will have different views and rules as to what is procedural and what is substantive and indeed different choice of law rules.