What exactly happens during a nuclear blast?

Let's say it's a relatively small and crude device where the radius of total destruction is about 3 miles. How far out would the shock and blast waves still be able to do physical harm to people and buildings and how far out would the shock wave be able to be felt without necessarily being hot or strong enough to hurt someone? Also, how far away could you be to this particular kind of blast and still be blinded by it but not killed and is the blindness always permanent?