ye , I did it I created an inventory ( with adsense enabled) and I got the code .
However , I dont get all the impressions of the website. Im gettin 6000 visits/day However on Adsense control panel it shows only 60 impressions from that website if when i filter ads by "Site" because on dfp i cant use channels.
Is there a reason you are trying to use DFP when you have no direct advertisers? Unless you are expecting direct advertisers I would suggest against using it. It can be a fairly complicated product to get setup properly. It will also prevent you from using adsense channels, adsense experiments, and differing syles for different sections of your site(s).
Since you don't have any advertisers there is no reason to setup any advertisers, orders, or creatives. To get AdSense to fill all unsold inventory you'll need to "enable for adsense" each of your ad units, enable targeting for each of your placements (if you want adwords advertisers to specifically be able to target your defined placements). Then configure and enable your default adsense settings under the inventory / network settings section.