Well, people usually dress up in suits or bunads (out national cloathing) and walk in some sort of a parade with norwegian flags and corps, through the streets. Since I live in quite a small town, the parade is'nt that much to brag about. Then we gather at a local house where the kids can participate in different games, like darts and potato runs, and win small prizes. In my town we use to have a very small auction, and some entertainment.
It can be different form where in Norway you are, but the parade is kind of a must. And of cource ICECREAM. Everybody eats icecream today. And when I was young I used to have competitions with my friends to see who could eat most icecream during the day. Old times...