If ads are in the RSS feed that is driving your newsletter then the ads should just show up, provided that you are not truncating the text in your emails before the ad displays.
You can add your own ads and sponsorships by using the advanced template editor. In order to do so, please start by clicking the “I Want To” button in the upper right are of the page.
From the drop down menu, please select “Template Design”.
Add your image and your link using the editor’s UI or by switching into the code view. Remember that scripts don’t work in email, so you need to use static images and links. Once completed you may choose to click the grey preview button before saving.