The Tariff Act 1988 is an Act to consolidate and amend the law relating to the imposition of tariff duty. In practical terms, it is one of the main laws behind import duty in New Zealand.
The starting point is section 3. It says duties must be levied, collected, and paid in accordance with the Tariff, or with a transitional safeguard measure, an emergency action measure, or a provisional transitional safeguard measure, depending on the case.
That makes the Act more than background law. It is part of the legal framework that supports whether duty applies to imported goods and what legal mechanism supports that duty.
At the same time, the Act does not stand alone. It works with the Tariff itself, with Orders in Council made under the Act, and with Customs legislation. If you import goods, you usually need to read those sources together rather than relying on this Act by itself.