Creating an Ad
It should be noted that a pre-requisite for creating an Ad is the creation of an Advertiser with instructions found here, a Campaign with instructions found here and lastly an Ad Group with instructions found here.
Once you have successfully created all three entities. Navigate to the AdGroups tab in the Advertising section as depicted below.
On this page you will find an index view of all Ad Groups created. Find the Ad Group that you wish to create a Ad for and hover over the section to the right selecting the Ads link shown below.
Once you're on that page, select the Create Ad button in the upper right corner which will redirect to a form.
This form should look like the image below. Simply fill out the name of your Ad, select the creative from the drop down and fill out any optional fields that are applicable.
You can set impression and click limits on this Ad, as well as boost the ad in the optimization algorithm by applying Boost or CPM override. You can also set a CPC price on individual Ads.
Once you are satisfied with your entry, click the Save Ad button and you will be redirected back to the Ads index view.