This note is composed of various concepts and definitions that helps to enhance the preparation for a module on macroeconomics. These concepts would be returned in consequent notes about this product. At the beginning, it describes the components of GDP and national income accounting, and examines the reasons of high focus on GDP by the economists. Later on, it examines the ways in which determinants of components of GDP communicate to the market, and how a model-that draws assumptions into results-can be helpful in forecasting the interest rates and GDP. This note also acquaints to students about the general economic modeling with the help of illustrations of how to evaluate endogenous variables from frameworks of equations and exogenous variables. At the end, it shows the role of assumptions in macroeconomics and by posting a portion of the assumptions that we will be incorporated in next technical notes.