iron mining hut near iron mine; just outside city walls, near outpost; settlers say they have nothing to do; mine full of iron ? thanks

Try demolishing the building, and then replacing it in a slightly different position next to the mine, you may have placed it in a way that prevents them getting to the mine.

Not sure about latter Settlers versions, but earlier ones you need to make one pick-axe (via the toolsmith/metalworker) to create a miner, and you also need to them food continually while they work.