These are clamps or supports to be fixed to the wall or wood board or other material. You will need screws or nails for fastening.

Then you will need to arrange PET bottles, such as 2L soda bottles, cut in half to fit into these clamps.

Keep making cuts in the bottles until the clamp can hold them firmly without the possibility of the bottle coming out.

The bottle is the shelf.

Depending on the shape of the bottle, you may need to adjust the distance between the clamps for the shelf to be very firm. 

Two clamps are needed for each shelf and each clamp requires 2 screws or nails to be fixed.