Partial dependence is a thought experiment you can run yourself: give every row the same value in one column, ask the model for its predictions, and average them. Repeat for each value you want to try.
A letting agent predicts monthly rent from [floor_area_m2, building_age_years].
Task: write average_prediction_at(rows, rents, column, values).
LinearRegression() on rows and rents.values, in order: copy the rows, set column column of every copied row to that number, predict all the copied rows, and take the mean prediction.