To create a placement:
In your DFP Small Business account, click the Inventory tab, then click Placements on the left-hand panel.
Click New placement.
Enter a placement name (naming tips) and description (optional).
Associate ad units to the placement by clicking include next to the desired ad unit. (You can complete this step later if an ad unit doesn't exist yet.) Each placement should include a unique combination of ad units.
(Optional) Select Google AdWords to make this placement available for AdWords advertisers to target (Learn more).
(Optional) To copy targeting settings from a pre-exisiting AdSense channel, click Copy AdSense targeting.