The tricky part.
Take one end and lift the dowl cross into a vertical position. Pull the length of paracord that attaches the shelves to the dowl tight, so the shelves at one are supported by the paracord. Tie each end off using the bottom hole at the bottom of the cross. Repeat for both sides.
The shelves should be free standing but they have no shear stiffness. Make two lengths about 2m (6ft) of paracord and diagonally thread the paracord through the remaining top and bottom holes to form an X, this shear web provides the shear stiffness that stops the shelves folding over sideways.