The article explains complex trade models like Melitz, Armington, and Krugman in a more detailed and extended way. It adds features like different regions, various costs, and factors affecting international trade. The researchers hope to make these advanced models easier to understand for students and reviewers. The study aims to show how reducing trade costs can impact welfare on a global scale. The article breaks down the equations used in these models, offering a guide for creating new international trade models that fit real-world data better. Balistreri and Tarr further applied these models to real data, exploring how different trade policies affect overall well-being in various trade scenarios.