Too Long; Didn't Read
Facebook's ad auction is a real-time process that occurs every time a user is eligible to see an ad. This happens when they open the Facebook app or website.
The bid amount, ad quality, and estimated action rates determine the ad rank. The winning ad is shown to users, and advertisers are charged based on auction dynamics.
Advertisers should focus on relevance and quality for better performance. Facebook's algorithm constantly refines ad delivery for a positive user and advertiser experience.