The study of Economics is divided into two distinct branches: Micro Economics and Macro Economics.
The word "micro" means very small. So micro economics implies study of economics at a very small level.
In a society comprising of many individuals collectively, every single individual makes just a small part. So the economic decisions taken by a single individual become the subject matter of micro economics.
What are the economic decisions an individual takes?
(a) In order to satisfy various wants an individual buys good and services. To buy goods and services the individual has to pay some price from his limited amount of income. So the individual has to make a decision with regard to quantity of the good to be purchased at given price. He or she has to also decide the combination of different goods to buy to get maximum satisfaction as a buyer.
(b) An individual also sells goods and services as a seller. Here he has to take decision regarding the quantity of good to be supplied at a given price so that he or she can earn some profit.
(c) Micro economics determines the price of goods and services in the market.
(d) In order to produce a good an individual producer has to take decision as to how to combine the various factors of production so that maximum output can be produced at minimum cost.
The word "macro" means very large. In comparison to an individual, the society or the country or economy as a whole is very large. So the economic decisions taken at the level of the economy as whole are subject matter of macro economics.
The government represents the whole country, not just any individual. So the decisions taken by the government are meant for solving the problems of the whole society. For example, government makes policies with respect to collection of taxes, expenditure on public goods and welfare activities, etc. which affect the whole economy. "How do such policies work" is the subject matter of macro economics.
In micro economics, you study the behavior of an individual as a buyer and seller. As buyer the individual spends money on goods and services which is called his or her consumption expenditure. If you add consumption expenditure of all individuals then you get idea of aggregate consumption expenditure of the whole society. Similarly aggregating incomes of individuals becomes total income of the country or national income. So study of these aggregates such as national income, total consumption expenditure of the country, etc. comes under macro economics.
Another example of macroeconomic issue is the study of inflation or price rise. Inflation or price rise does not affect an individual only, but it affects the whole economy. So knowing its causes and effects as well as controlling it, come under the study of macro economics.
Similarly, problem of unemployment, economic growth and development, etc. concern with the whole population of the nation and hence are covered under the study of macro economics.