New Zealand does not have a document called the constitution. Rather it draws together an "unwritten" or "Westminster-style" constitution from various acts (including various English acts predating the English colonisation of the country eg Magna Carta), judicial precedent (case law), prerogative powers, conventions, political custom and public international law.
The constitution of independence: the development of constitutional theory in Australia, Canada and New Zealand by 
The Treaty of Waitangi in New Zealand's law and constitution by New Zealand is a constitutional monarchy and parliamentary democracy.
The Head of State is King Charles III New Zealand who, on the recommendation of the Prime Minister, appoints a personal representative, the Governor-General, to fulfil the official and ceremonial roles. Governor-Generals of New Zealand are non-partisan and not involved in active government.
The legislature is a unicameral parliament, officially called the House of Representatives.
The executive government is the Prime Minister and Cabinet. (It is sometimes referred to as the Crown.) The PM and their cabinet must first have been elected to parliament - since the adoption of mixed member proportional system of voting (1993) coalition and minority governments have become a feature.
Māori (NZ's indigenous people) have the right to choose whether to vote in a general or a Māori electorate. The number of Māori seats in a parliamentary term can change, reflecting the strength of the Māori electoral roll.
The official languages are English, Māori, and New Zealand Sign Language.
Law Alive : the New Zealand legal system in context by The New Zealand Geographic Board Ngā Pou Taunaha o Aotearoa has the task of assigning official names to places and significant features in New Zealand and in the Ross Sea region of Antarctica.