Every placement has an initial ad group type that was selected when the placement was first created. If you’d like to rotate different types of ads within a placement, you can create another ad group within the placement and the different ad types will automatically rotate. For example, if you originally created a placement to include text ads, but now you’d like to rotate those text ads with video ads, you’ll have to create another ad group with the group type set to “Video Ads”.
Creating ad groups is also helpful when setting targeting conditions within your placement. If one ad group has targeting conditions set, you will also need to create another ad group with the inverse targeting conditions (recommended) or no targeting conditions. If this is not done, you run the risk of being charged for an impression without serving an ad.
When creating a new ad group, go to the “Placement Details” screen and click the “Create” button located towards the top left section of the page. Enter the name, the ad group type, the ad group status, and the distribution weight or impression order. Finally, click on the “Create” button so the group is successfully added into the system and appears in the “Ad Groups” list. You can also make recycling ad groups.