I'm at this page and have no idea what this means. It is telling me to choose 5 custom channels to track the performance of my ads ?
You can tracks you ads through well dedicated channels! suppose if you are using adsense in multiple sites then you can create different channels and re-generate codes using channels as a results you can easily track daily & monthly earnings! that from which channel/site giving you good earnings! Its a good way to track earnings of multiple sites!