If the Price is high, then the Demand will be low. I.e. the Quantity Demanded will be Low. As Price falls so Demand increases.

The Quantity Supplied will be determined by Price-provided there is a Demand, the higher the Price the greater will be the Quantity Supplied as more manufacturers enter the market place to make a profit.

Demand and Supply will come into equilibrium point at say A when the Quantity Supplied will be exactly taken up by the Demand in the market place for that Price.

If Demand or Supply changes then there will be a different line for Supply and for Demand meeting at a new point of equilibrium B.

The slope of the Demand curve is a measure of Elasticity, I.e. the extent to which Demand is altered by a change in Price. Maximum elasticity is when the line is at an angle of 45 degrees.

In Rationing there is a fixed Quantity supplied,Taxation adds a fixed sum to the Market Price.