1. Navigate to the AdWords Web site and log in to your account.
2. Select the 'Campaigns' tab at the top of the page once you have successfully logged in.
3. Choose from your advertising campaigns the one that contains the advertisement you'd like to add to a specific site. If you have not created any advertising campaigns yet, select the 'New campaign' button and follow the steps to create your first campaign.
4. Select the 'Networks' tab located underneath your campaign name, to the left of the 'Ad groups' tab.
5. Find the row marked 'Display Network.' Immediately underneath this row, click on 'show details' next to 'Managed placements.'
6. Click on the 'Add placements' button to bring up a text box labeled 'Add managed placements.'
7. Type in or copy and paste the URL of the site you would like to place your advertisement on in the text area labeled 'Add managed placements.' Remove the 'http://www.' portion of the URL before putting it in the box and include only one URL per line if you'd like your ad to appear on multiple sites. Select the 'Save' button below the box once you have finished entering the sites into the text area. Your ad will run on the sites you selected.