Summarise in own words:

Article 12
Preconditions to the exercise of jurisdiction
1. A State which becomes a Party to this Statute thereby accepts the jurisdiction of the Court with respect to the crimes referred to in article 5.
2. In the case of article 13, paragraph (a) or (c), the Court may exercise its jurisdiction if one or more of the following States are Parties to this Statute or have accepted the jurisdiction of the Court in accordance with paragraph 3:
(a) The State on the territory of which the conduct in question occurred or, if the crime was committed on board a vessel or aircraft, the State of registration of that vessel or aircraft;
(b) The State of which the person accused of the crime is a national.
3. If the acceptance of a State which is not a Party to this Statute is required under paragraph 2, that State may, by declaration lodged with the Registrar, accept the exercise of jurisdiction by the Court with respect to the crime in question. The accepting State shall cooperate with the Court without any delay or exception in accordance with Part 9.

Article 12 outlines the conditions that must be met for the International Criminal Court to exercise its jurisdiction over crimes specified in Article 5 of the Statute. This includes the acceptance of jurisdiction by a State that becomes a party to the Statute, as well as the involvement of the State where the crime occurred or where the accused person is a national. States that are not parties to the Statute can also accept the Court's jurisdiction for a specific crime by lodging a declaration with the Registrar. The accepting State is required to cooperate with the Court without delay or exception.