Ragnar Frish have divided the whole economic theories into two parts - Microeconomics and Macroeconomics. These two words were first used by Ragnar Frisch in 1933. Since then, the whole economics analysis is carried dividing it into two parts.

Microeconomics is the study of decisions made by people and businesses regarding the allocation of resources and prices of goods and services. It also takes into account taxes and regulations created by governments.
Microeconomics focuses on supply and demand and other forces that determine the price levels in the economy. It takes what is referred to as a bottom-up approach to analyzing the economy. In other words, microeconomics tries to understand human choices and resource allocation.
Having said that, microeconomics does not try to answer or explain what forces should take place in a market. Rather, it tries to explain what happens when there are changes in certain conditions.
For example, microeconomics examines how a company could maximize its production and capacity so that it could lower prices and better compete in its industry. A lot of microeconomic information can be gleaned from the financial statements.
Microeconomics involves several key principles including (but not limited to):
Demand, Supply, and Equilibrium : Prices are determined by the theory of supply and demand. Under this theory, suppliers offer the same price demanded by consumers in a perfectly competitive market. This creates economic equilibrium.
Production Theory : This is the study of production.
Costs of Production : According to this theory, the price of goods or services is determined by the cost of the resources used during production.
Labor Economics : This principle looks at workers and employers, and tries to understand the pattern of wages, employment, and income.
The rules in microeconomics flow from a set of compatible laws and theorems, rather than beginning with empirical study.
Macroeconomics , on the other hand, studies the behavior of a country and how its policies affect the economy as a whole. It analyzes entire industries and economies, rather than individuals or specific companies, which is why it's a top-down approach. It tries to answer questions like "What should the rate of inflation be?" or "What stimulates economic growth?"
Macroeconomics analyzes how an increase or decrease in net exports affects a nation's capital account, or how GDP would be affected by the unemployment rate .
Macroeconomics focuses on aggregates and econometric correlations, which is why it is used by governments and their agencies to construct economic and fiscal policy. Investors of mutual funds or interest rate-sensitive securities should keep an eye on monetary and fiscal policy. Outside of a few meaningful and measurable impacts, macroeconomics doesn't offer much for specific investments.
John Maynard Keynes is often credited as the founder of macroeconomics, as he initiated the use of monetary aggregates to study broad phenomena. Some economists reject his theory, while many of those who use it disagree on how to interpret it.