The Browser contact the Ad Server with an AdTag (code snippet) - It's a little tag that defines what ads to put on the site or app.
AdTag has parameters that permits to lookup the ads
The server looks to all ads available based on the browser and ip address
When it find one, it counts an impression tracking that the ad has been served
Rendering
How would a company know about a third site and that the consumer visits it regularly?
The Agency had put the young male sports fan segment into their own Demand Side Platform, or DSP
The DSP is plugged into the Ad Exchange
The DSP is looking to buy an ad impression that will enable it to present an advertisement to young sports enthusiasts, a market segment or audience to which Pete belongs.