Most Thai recipes count each double leaf as two separate leaves. Frozen kaffir lime leaves are a good substitute for fresh. Dried leaves are much less flavorful, so use twice as many as the recipe calls for if you're substituting them for fresh leaves. It has a strong, minty, peppery flavor. It's sold in bunches with lots of pointy leaves on each stem.
Thai cooks toss it into soups, salads, and noodle dishes.
Remove the outer leaves, then use about six inches of the base, discarding the top and the very bottom. It's best to cut lemongrass into large pieces that can be easily removed after the dish is cooked. The Japanese use this to flavor soups and salads. Look for plastic bags of folded leaves among the frozen foods in Asian markets. Koreans use them to wrap packets of meat or as a fresh herb.