This document discusses general equilibrium models using input-output analysis and its relationship to aggregate demand and supply. It covers the five main sectors in an economy - households, firms, government, foreign trade, and financial - and how they interact. The firm sector produces goods equal to total expenditures. Households receive income and allocate to consumption and savings. Government balances spending and taxes. Foreign trade balances exports, imports and borrowing. Financial sector balances investment and national savings. It also discusses how input-output matrices can model intersectoral flows and the total interrelated economic system.