1. Kia ora: This is the most common and versatile greeting, meaning "hello", "good morning", "good afternoon", or "good evening". It's appropriate for almost any situation.
2. Tena koe: This is a more formal greeting, literally meaning "Greetings to you". It's often used when addressing someone older or in a position of authority.
There are other ways to say hello depending on the time of day or the context, but these two are the most common and versatile.