You’ll need to customize the Adsense code in the plugin itself. Look in the adsense.php file. In the first function there’s a block that says “Begin Google Adsense code”. You want to replace the lines between that line and the one that says “End Google Adsense code” with your actual adsense code provided to you by Google. Otherwise, you’ll be showing ads for me.
Once you activate the plugin, you should notice a new button on your Quicktags toolbar. The new button is “Adsense”, and it works like “more”. Click it to insert the Adsense tag, and enjoy the newfound wealth.
