Thanks for purchasing a CSSU… as described, each unit is hand-made and custom designed. We’re not IKEA yet, but do hope to make assembly as simple as possible. Reading the below and reviewing applicable pictures will certainly help.
When assembling the CSSU and the installation will be a permanent one, a small bit of adhesive caulk — either clear acrylic (easy water clean up) or silicone (careful alcohol cleanup) can help to secure the feet to the legs. Also a small bit inside each screw hole — both on the feet and on the shelves — will improve the bite and hold of the screws.