To generate tags for one or more ad units:
In your DFP account, click the Inventory tab.
Click Generate tags on the left-hand panel.
Select ad units by clicking Add next to the appropriate ad unit names. (You may generate tags for all ad units at once or page by page.)
Click Generate tags. A text field appears, containing the full HTML for the page, including the selected ad units.
Follow the comments in the HTML to cut and paste the code into your page.