Step 1: Attach nail
The first step is to hammer a nail into the wall. I was not allowed to, but luckily there were two nails already in that wall. So I decided to do a hanging shelf on a single nail. To hold it steady sticky tape was fixed to the wall at strategic locations. This helps the shelf stay in place even when loaded unevenly.
Step 2: Add shelves
Step 3: Load it up
You can attach various other storage units to this, limited only by the carrying capacity of that single nail.