Feedback of Sell-in_Stock-In forecasting training exercise

Q1:I understand the demonstration of Sell-in_Stock-In forecasting (1star = not at all, 5stars = very well)

Q2:Which part do you have difficulty to understand? Please describe

Q3:I can do the exercise of Sell-in_Stock-In forecasting (1star = cannot do, 3stars = can do it but need some help, 5stars = can do it totally independently)