D₀ is the original demand curve. A shift to D₁ (rightward) represents an increase in demand: at every price, consumers want to buy more. A shift to D₂ (leftward) represents a decrease in demand: at every price, consumers want to buy less.
At price $20,000: on D₀ the quantity demanded is 18 million (point Q). After a rightward shift to D₁, quantity rises to 20 million (point S). After a leftward shift to D₂, quantity falls to 14.4 million (point T). These are all different curves, meaning different demand schedules, not movements along one curve.
At the higher price of $22,000, point R on D₀ shows 17 million demanded. Moving from Q to R is movement along D₀ caused by a price change. Moving from Q to S is a shift of the curve caused by non-price factors like income, tastes, expectations, or the price of related goods.