The only way I know to get your channel ID is to create a cahnnel ad then go to the code and you will see an ID # this is your channel ID. This is great for checking how a paticular campaign is progressing.
If you run adsense on two sites, you can set up two different channels one for each site that way you can see which site is performing better. Also if you are trying different ad type/placement on a site, you can set up a channel to see how ad type/placement is working and pick the best performer.
Channels are used to watch TV, You turn your TV and the you are able to tune them up j/k, follow what Smyrl says
When you get the channels figured out, play around with them from week to week. I have really increased my CTR by pating attention to what ad placements work and which ones are lousy. The system can look a little intimidating at first but after a while you will get the hang of it.