I could see these being useful out in the garden, camping, anywhere you cant drill into a wall but the ceiling would be OK, great for inside closets too.
Step 1: Get yer shelves
Step 2: Your needs
some suitable rope or other linear element (chain would be nice)
A lighter to finish your ends if your rope is the melty kind
a stool or step ladder
a measuring stick or tape
Tie up your ropes from 4 points, preferably on intended site, use hooks and stud finder as needed if you dont have a handy beam like I did.
Use the ladder or stool to position your shelf near where you want it to end up so you can tie it with greater ease.