The Posten Norge, or Norway Post, is accessible online and has helpful links to changing your address, cost of postage, customs, and more. The Post is owned and operated by the Norwegian Ministry of Transport and Communications. There are about 1,500 post offices and over 30,000 postboxes.
Stamps can be purchased at: Post offices, in-store post offices and postbutikken. Letters can be mailed from: post offices, in-store post offices, rural postal service and in red or yellow letter boxes.
Prices for letters range from 8 NOK to 12 NOK with a maximum weight of 2 kg. A complete price list can be found at: http://www.posten.no/en/Products+and+services/Letter+services/1091.cms.
Letters are usually addressed formally. Here is an example:
Herr Hans Hansen