Want to know more on AdSense URL/custom channels then here is the must watch video tutorials from Google Official AdSense Channel.

Tutorial 1:

How to use URL channels to track the ad performance of specific pages and sites in AdSense by Matthew from the North America AdSense team.

Tutorial 2:

How to use custom channels to track the performance of specific ad units by Boyar from the North America AdSense team

Tutorial 3:

How to turn your custom channels into targetable ad placements. This feature allows advertisers to bid on specific ad units on your pages, and the descriptions you create will help them understand more about your site by Laurence from the North America AdSense team