This chapter introduces the fundamentals of Econometrics, which combines economic theory, mathematical modeling, and statistical inference to analyze real-world economic data. It provides a structured framework for understanding complex economic phenomena such as consumer behavior, inflation, growth, and market dynamics. Econometrics play a key role in quantifying relationships between variables, enabling predictions and informed policy decisions. Originating with Frisch in 1926 and advanced by the scholars Tinbergen, Klein, and Kuznets, the field emphasizes data analysis and hypothesis formulation based on economic theory. Modeling is central to Econometrics, it clarifies relationships, tests hypotheses, and supports forecasting and strategic planning. This chapter focuses on the procedure of model testing using the Ordinary Least Squares (OLS) regression technique.