Action Details
Requirements and how-to articles for Google Ads's action:

paid action
A brand-centric format that performs well when placed non-intrusively alongside content on the left- or right-hand side of the page. This format integrates well with the content and layout of most sites, and provides advertisers with the ability to create engaging, creative content within this ad unit. Suitable for text ads and display ads. (Note: While demand from advertisers for larger ad formats is on the rise, the supply of available display ads for this ad size is currently limited.)

You need this to get it done:

You can create a responsive display ad, or upload a display ad. You can also choose to copy existing ads.
You can upload image ads as .gif, .jpg and .png
You can upload AMPHTML ads as a .zip containing 1 HTML document and up to 39 media assets.
Maximum file size: 150KB
Dimensions: 300 x 1050 pixels
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How-To Articles
A list of useful links for you:

Google AdSense Help - Guide to Ad Sizes
List of different ad sizes and how well each one performs.
Link missing here or found errors? Improve How-Tos