What is the meaning of the red and green lines connecting the black dots on the App's adjustment screen?

Black dots represent the electrodes, while the lines represent the connections among the electrodes. Red means NO connection. Green represents good connection of the electrodes to the scalp. The more green lines you get the better the device will provide the right stimulation to regrow your hair.

Only 80% of green lines is needed to start a session. Electrode-scalp connection increases over time and can reach (but doesn't need to reach) up to 100%.