With WordPress you can easily add your AdSense code to your blog. In order to do this, first login to the administrative end of your website. Then, go to the Appearance -> Widgets menu.
In this page select to drag-and-drop a Text widget onto your Blog Sidebar.
Then you should add a title (in our case - Advertisement) and under it, click the Text tab and then paste the actual code that you have obtained from Google. Finally, click on the on the Save button.
The ad will automatically be saved and appear in your WordPress Sidebar.