Economics is the study of how societies allocate scarce resources to produce goods and services. It has two main branches: microeconomics examines decision-making by individuals and firms, while macroeconomics looks at the economy as a whole. Key concepts include scarcity, choice, and opportunity cost. The four factors of production are land, labor, capital, and entrepreneurship. Graphs are used to show economic relationships, and shifts in curves occur when a third variable changes. Production possibilities curves illustrate the tradeoffs between different goods based on available resources. Points inside the curve represent inefficient production, while points on or outside the curve are unattainable due to scarcity.