The cellular canvas displays the evolution of a cellular automaton, with the horizontal axis being space and the vertical axis being time, flowing from top to bottom. A cell with a yellow dot is called a "control cell". You are free to set the state of any control cell. Doing so adds or updates a rule specifying the propagation of the cellular automaton.

In paint mode, you can set the paintbrush state with the buttons at the bottom of the screen, or the number keys (1, 2, or 3). Then click and drag across control cells to set their states to the paintbrush state.

In interpolate mode, click on a control cell and drag your cursor to smoothly interpolate between different states for that cell. The displayed evolution of the cellular automaton interpolates accordingly.