The two main ad formats that can be used in a Google Display Ads campaign are Responsive Display Ads and Uploaded Image Ads.

Responsive Display Ads allow you to upload multiple assets like images, headlines, logos, and descriptions. Google’s machine learning algorithms then automatically generate ads in different combinations and formats, and continuously optimize them over time. This enables a wider reach as Google adjusts the ad size, appearance, and format to fit available ad spaces.

Uploaded Image Ads, on the other hand, allow you more control over the design of your ads. You can create and upload your own ads in different layouts and sizes. However, you need to abide by Google’s creative guidelines and make sure you upload all the necessary sizes to maximize ad placements across the Google Display Network.

There’s also a third format, text ads, which are simpler in format and appear in text form but those are less common in comparison to the aforementioned ones. You could be innovative in deciding which formats to use based on your specific campaign goals and target audience, or even use a mix of all.