The document discusses consumer behavior and equilibrium using budget lines, indifference curves, and the marginal rate of substitution. It explains that a budget line shows the combinations of two products a consumer can purchase given their income and prices. Indifference curves represent combinations of goods that provide equal utility. Consumer equilibrium occurs at the point where an indifference curve is tangent to the budget line, where the marginal rate of substitution equals the slope of the budget line.