If you use promoted listings (which I suggest you do), this is where you can track your performance. View your impressions, base sales, promoted sales, and track how promoted listings are helping your business.
I always use promoted listings even if it’s only with 1% ad rate. I have noticed a boost in sales even using such a low percentage. Obviously, the higher the percentage the more favorable your listing is to be promoted by Cassini (eBay’s search algorithm).
This is also where you find the “Markdown Manager” on the left side menu. You will use this to create markdowns for products or groups of products.