From the begining.Economics.

Economics : the study of how to allocate scarse resources in the most effective way.
For example- some people are rich to buy everything they want, but some people are not, so they have to choose what they need and what they can afford themselves to buy. The main thing in economics is CHOICE.

Economic problem: how to allocate scarce resources among alternative uses.
Not only individuals can face this problem, but also firms have to decide what to produce and how to produce in the most efficient way.

So there are 2 traditional fields of economics: mircoeconomics and macroeconomics.
Microeconomics: the study of how households and firms make dicisions in markets.
(Household:group of people whose spending dicisions are connected.)
Macroeconomics: the study of issues that effect economies as a whole.