The document provides an overview of display advertising basics, including the key players and how impressions are bought and sold. It discusses demand side platforms (DSPs) that enable real-time audience buying on ad exchanges. Ad exchanges are marketplaces where publisher inventory is sold to advertisers/agencies via auctions. Sell side platforms help publishers manage their inventory and route ads to exchanges. The document also summarizes how real-time bidding works, with bids happening in milliseconds before an ad is viewed, and how data management platforms compile audience data to help target ads.