Study in New Zealand website(external link) provides international students with information and resources including links to institutions and courses(external link) and scholarships(external link) and a guide to living and studying in New Zealand(external link).
Student visas
Immigration New Zealand has information about how to apply for a student visa(external link).
If the length of the course you are planning to study is designed to last for longer than 3 months, you must apply for a student visa, regardless of how long you plan to study in New Zealand.