Structures are composed of combos (which can be edited via the Combo Editor). Screens are, in turn, composed of structures, so changes made to a structure will be reflected in each screen that contains that structure. Each level has its own set of structures.

To edit a structure, select a combo on the left and use to mouse to paint it onto the structure. You can also edit the shape of a structure by joining and splitting rows and shifting rows to the left or right, although you may not add or remove additional tiles. Right-click on a row in the structure to bring up a menu with all the options for moving, joining, and splitting rows.