The article develops tools to analyze auctions and their impact on welfare and revenue. By separating the analysis into two parts, it shows how bidders' contributions affect welfare and revenue in different auction scenarios. The findings suggest that in certain auctions, the revenue generated is a good approximation of the optimal revenue. For example, in a specific type of auction, the revenue is at least 3.16 times the revenue of the optimal auction. The study also provides insights into auctions with reserve prices and different auction formats. Overall, the research sheds light on how auctions can affect welfare and revenue outcomes.