Find the UET tag in the body section of this webpage. UET tags can be anywhere on a webpage (on this webpage its in the body section)
In the head section (before the closing head tag)
In the body section (before the closing body tag).
As your webpage loads, it triggers the UET tag that results in HTTP requests. The most important request is to bat.bing that looks like http://bat.bing.com/action/0?ti=.... This request tells Bing Ads about the user visits to your webpage. You can use tools like Fiddler to monitor all the requests that your browser is making when your webpage loads.
Please refer to Bing Ads help documentation for more info on UET and why it is important for Conversion Tracking and Remarketing in Bing Ads.