This plugin doesn’t generate the adsense code block for you. It wouldn’t make much sense since Google does it for you.
To generate an ad block code, you need to login into your adsense account and go to the “My Ads” section (here a link). You will then see different ad blocks and can click on “Get code” to get the code corresponding to a particular ad unit.
If the list is empty, you need to create an ad unit by pressing the “New ad unit button”.
Once you have the code, you can use this plugin to display the different ad units in different parts of your site.
Hope this helps.