Here are 2 sites that will help you out. The diynet site looks like a good way to install the shelves. When I first took a quick look it didn’t make sense. But then I realized they turned the L shape bracket on its side and screwed it in the underneath hollow part of the shelf and then attach it to the wall.
So instead of the shelf sitting on the flat part of the bracket were you would be able to see it either going up the wall behind the books or down the wall below the books, it’s now turned on it’s side so the shelf rests on the sharp side edge.