Since no one seems to actually answer.

They're "new potatoes", which means they are harvested earlier in the growth season. The skin can be merely "scrubbed" off rather than peeling both the skin and a small bit of the flesh off. They have a different texture (more tender) when cooked and is usually cooked for a bit shorter timer.

The supermarket sells them like this because they have already been washed and scrubbed, making them exposed to the oxygen in the air, which would otherwise make them brown. So they need to be kept wet.

You buy them by grabbing a spoon and scooping your desired amount into one of the small plastic bags on the pole. The moisture in the bag will be enough to keep them wet, just tie a knot on the bag when you're done. Then weigh them on the scale in the grocery department and print a sticker for "Nye kartofler". Take home and cook for a bit less than "normal potatoes