The Capital Asset Pricing Model (CAPM) illustrates the relationship between expected return and risk of a security, calculated using the formula ra = rrf + [ba * (rm – rrf)]. It emphasizes the need for a risk premium, compensating investors for systematic risk, and is crucial in determining the weighted average cost of capital (WACC) in financial modeling. CAPM is essential for evaluating investment returns, net present value, enterprise value, and equity value.