If you are creating a 'L' Shape or an 'U' shape with your shelving, but you are not using corner shelf kits, then you will need corner supports.
These supports are for use when creating a 'Butt' fit with the shelving. Which is simply bringing a shelf from a side wall to meet a shelf along the back wall. In order to get the correct support in the corner you will need to fit one of these steel supports.
You will need one for every corner you create, so if you are creating two tier hanging which you intend to bring around the corner, you will need two corner supports.
The supports come with instructions and are each sold separately.