"Measuring aggregate production and income" - Krugman et al. Essentials of Economics. Chapters 14 and 15
"An aggregate supply-aggregate demand model" - Krugman et al. Essentials of Economics. Chapter 16
"Financing the economy" - Krugman et al. Essentials of Economics. Chapter 18
"Economic policy" - Krugman et al. Essentials of Economics. Chapters 17 and 18