Demand

Demand is the amount of a good/service that a consumer is willing & able to purchase at a given price in a given time period.

As you can see here , this is the report of milk ,

this is the example of law of demand 

Effective Demand

Effective demand is where the willingness to buy is backed by the ability to pay. For example, when you want a laptop but you don't have the money, it is called demand. When you do have the money to buy it, it is called effective demand. The effective demand for a particular good or service is called quantity demanded.

Difference Effective Demand and Demand 

Demand is different from want or need want / need means having the desire for a good or services without the ability to pay for it. Effective demand refers to desire backed up the ability to pay for the commodity.