If you’re planning to study in New Zealand full time for more than three months you’ll need a student visa.
Student visa requirements include:
an offer of place from an educational institution approved by the New Zealand Qualifications Authority
a written guarantee from an institution or person that suitable accommodation is available to you in New Zealand (if you're under 18 years)
evidence of sufficient funds to live on while you are studying
a return air ticket to your country, or evidence of sufficient funds to buy one.
If you’re spending six months or more here in New Zealand you may need to be screened for tuberculosis.
If you’re over 17 and intending to be in New Zealand for over two years, a police certificate will be required to show that you are of good character.
If your course is three months or less, you don’t need a student visa: just a visitor visa.