The list of indifference curves associated with different utility level is called an Indifference Map. The rational consumer prefers the higher or right most, Indifference curve, since they represent combinations of goods providing higher utility levels.
The slope of the indifference curve is called the marginal rate of substitution. It is the rate at which consumers are willing to give up one good in exchange for more of the other good. For most goods the marginal rate of substitution is not constant so their indifference curves are curved. Indifference curves are typically assumed to have the following features:
Today's Economy is market driven where customer is the king. The market price is determined by forces of 'Demand and Supply'. To excel in the market, the firms must asses the demand of the customer. Consumer theory uses indifference curves and budget constraints to produce consumer demand curves. A budget constraint shows the consumer's purchase opportunities as every combination of two goods that can be bought at given prices using a given amount of income. Consumer's optimal combination of goods to consume is the amount that maximizes his utility subject to his/her budget constraint.