To amplify on what ChrisMwn said, you have two years' travel conditions issued with your Residence visa. The travel conditions are what allows you to come and go freely from NZ as many times as you like, and they're the only part of what you have just received that stops after two years. While you're inside NZ, your Residence visa allows you to stay and work there permanently.
To go on being able to travel after the travel conditions run out, you have to get a PR visa, which you can apply for when you've had Residence for at least two years, and the "184 days (cumulative) in each of the two 12 month periods preceding the date of application" he mentions is the most commonly used way of qualifying for that. (You're proving commitment to NZ.) Full details here.
http://www.immigration.govt.nz/migra...quirements.htm