The RMA requires councils to create plans that help them manage the environment. These plans contain all sorts of rules and conditions for activities that might affect the environment.
Plans, usually through rules, state whether an activity is permitted, meaning you can do it as of right, or whether it requires a resource consent. When the council considers your application for resource consent, it follows the processes set out in the RMA.
A regional plan is created by a regional council. It concerns issues that affect the coast, air, water or land. Regional plan rules cover things such as the construction of jetties, and the discharge of wastewater from a factory into a waterway.
A district plan is created by a city or district council. It concerns the management of land-use and subdivision in a city or district. District plan rules cover things such as noise and the location and height of buildings.
Sometimes you'll need to apply for a resource consent from both the regional and district/city council.