Hi cscgal,
You haven't missed too much. This feature has only been around for only a couple of months. As you figured out, the content bids are set at the Adgroup level in each campaign. You can bid as low as $0.01. But, that's no guarantee your ad will display impressions. First you need to edit your campaign settings, then, you need to go into the individual adgroups to bid separately for clicks in the content network.
My experience is that the CTR is high, and conversions low for the Content Network. IMO, the content network is best for branding. Not, ROI.
Another alternative to Google's content network, is setting up a Google Site-Targeting Campaign. Site-Targeting is just another way of advertising on Google's content network. But, you get to choose which sites your ad will run on. And you have the option to display an Image ad. You can also place tracking code on the destination url.
I hope that helps:-)