Earth Cone is designed with four side flaps. The two long ones have locking tabs at each end while the two corresponding shorter ones have insertion slots cut out near the fold lines - see images below.
To erect, it is as easy as folding the cone into shape with help from the pre-scored fold lines. Next, push the locking tab completely through the corresponding slot with your thumb, as seen below.
Once the tab is pushed all the way through, you can feel it locked in place. The magic is that the tabs are slightly wider than the slots - very simple and effective!