To change an input to a border cell, simply click on the input line (inward-pointing arrow) in the cell matrix picture. Blue lines are D inputs, red lines are C inputs. If an input is set to 1, the corresponding line will be bright. If the input is 0, the line will be dark. If any of a cell's C inputs is set to 1, the cell enters C mode. This is indicated by a change in the color of the cell. Only border cells' inputs can be changed by the user. Internal cells' inputs are controlled by their neighbors' outputs.
In addition to the large truth table at the right of the display, each cell displays a small iconic representation of its truth table within the gray square inside the cell. Dark dots correspond to 1s, and light dots correspond to 0s. This display is most useful for noting the shifting of a cell's truth table, rather than actually reading the input-to-output mapping. Modify a cell's truth table via the separate truth table.