Welcome! You're seeing a simplified geologic map of Earth. At the top you can modify the shading to reflect either rainfall or hillslope and you can change the annual volcanic outgassing (V).
At the bottom you'll see the key to Earth's different rock types. You can select one and start painting over the current geologic map of Earth. In doing so, you'll alter Earth's weatherability.
When you're ready to calculate the new steady-state pCO2, just press the CALC button in the top left.
Contact me with any questions or feedback! - Josh