Google AdWords Ad Extensions Basics

Google AdWords extensions give potential shoppers more information about a merchant and more options to engage with that merchant before clicking a search ad.
Although ad extensions have been around for a couple of years, Google recently added conversion tracking data to extensions, making it significantly easier to measure extension performance relative to actual sales.
This addition to Google's pay-per-click ads appear when ads are displayed in Google search results and on select search and display network partners' sites. Although these is no charge for adding extensions to an ad, click-through charges still apply.

Campaigns and Ad Extensions

In AdWords, ad extensions are associated with individual campaigns. To see ad extension options or create new ad extensions, log in to an AdWords account.
Navigate to the “Campaigns” tab. Next, choose the “Ad Extensions” tab in the middle of the page.

Google AdWord ad extensions are applied at the campaign level.

If there is not an ad extensions tab visible, click the "down arrow" icon at the end of the row and add the extensions tab.

The ad extensions tab may not be immediately visible.

From this screen, a user may add any of the several ad extensions that Google currently offers.

                        There were five ad extensions available at the time of writing.


source:practicalecommerce.com