Here you can choose between responsive (automatic size) ad unit and fixed sizes. In general, wider ad units perform better. In most cases you can choose responsive ad unless you want a fixed size ad. In such case choose one of recommended ad sizes, which have shown to perform well across a variety of sites. Ad sizes that perform well on mobile are shown with a mobile icon.
WordPress (WordPress.org) is a free and open-source content management system (CMS) based on PHP and MySQL. Features include a plugin architecture and a template system. It is most associated with blogging but supports other types of web content including more traditional mailing lists and forums, media galleries, and online stores. Used by more than 60 million websites, including 30.6% of the top 10 million websites as of April 2018, WordPress is the most popular website management system in use. WordPress has also been used for other application domains such as pervasive display systems (PDS).