During the very first stage you install the necessary ad server access script on your website. This dynamically pulls ads from the server's database into a cache file on your website. The individual weight of each participant determines the chance of their ad being displayed. Then, each time a page of yours is requested, the script pulls the ads from this cache file and displays it in the browser.
From the moment you create an ad in your account and after it has been approved by a human reviewer, it can take up to 100 hours for the ad to be displayed to its full potential on the other websites.
You can create a limited number of ads (20 at the time of writing) and assign a user-defined amount of available weight to it. See Ad Management for more info. This way you can decide which ads should get more exposure than others. Writing multiple ads also allows for testing which one converts best and allows you to target multiple key phrases for their possible link popularity. See Pre-installation Thoughts for advertising strategies.