The document discusses aggregate expenditures and the aggregate demand model. It provides an example where an increase in planned investment of $100 billion leads to an increase in real GDP of $500 billion through a multiplier process. As households spend a portion of additional income, this stimulates further rounds of spending. The multiplier captures how an initial change in spending is amplified through subsequent rounds of consumption. A higher price level reduces consumption and planned investment, shifting the aggregate expenditure curve inward and lowering real GDP demanded.