Do lightning rods attract or repel lightning or simply provide a conductor which minimizes damage for the occasional lightning strike of a building? Seems like its difficut to find out if or why they work.

They provide a conductive route to ground that goes around buildings rather than through them.

The intent is to attract lightning ad shunt it safeky to earth. By putting a grounded rod above the level of the structure you're protecting, the rod is more likely to get hit by lightning than the structure.