Summarise in own words:
Article 21
Applicable law
1. The Court shall apply:
(a) In the first place, this Statute, Elements of Crimes and its Rules of Procedure and Evidence;
(b) In the second place, where appropriate, applicable treaties and the principles and rules of international law, including the established principles of the international law of armed conflict
(c)Failing that, general principles of law derived by the Court from national laws of legal systems of the world including, as appropriate, the national laws of States that would normally exercise jurisdiction over the crime, provided that those principles are not inconsistent with this Statute and with international law and internationally recognized norms and standards.
2.The Court may apply principles and rules of law as interpreted in its previous decisions.
3.The application and interpretation of law pursuant to this article must be consistent with internationally recognized human rights, and be without any adverse distinction founded on grounds such as gender as defined in article 7, paragraph 3, age, race, colour, language, religion or belief, political or other opinion, national, ethnic or social origin, wealth, birth or other status.