What does a market demand curve predict?

I believe economists create demand curve to predict how people will change their buying habits when prices change. A demand curve is plot of Quantity of products or services demanded in the market against the prices for a given period of time. The price appears on the horizontal axis and the quantity demanded on the y axis. The demand is the quantity of goods or services that the consumers are willing and able to buy at a given period of time.  

Explanation:

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the act of deciding on matters of the economy. economic decision making is routinely conducted by finance ministers, economic advisors, heads of major central banks and business leaders and can have profound effects on a major economy.