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1. They’re Google Ads from AdSense. Once you become an advertiser through Google you’d insert your bar code somewhere in to your navigation div tag (and adjust your CSS).
2. The plugin can be found here.
3. That theme is free and you can get it here.

As I say you would put it in to the div navigation (header.php) to get it up there at the top, but you will need to adjust the css (style.css) yourself as the theme won’t have been designed with Google Adsense in mind.