Ratio analysis involves calculating financial ratios to analyze a firm's performance. There are several categories of ratios, including liquidity ratios, activity ratios, debt ratios, profitability ratios, and market ratios. Liquidity ratios measure a firm's ability to meet short-term obligations, activity ratios measure how efficiently a firm uses its assets, debt ratios indicate the degree of a firm's financial leverage, profitability ratios evaluate profits relative to sales and assets, and market ratios relate market value to accounting values. Ratio analysis provides insights into a firm's financial health and performance.