To create a campaign from a template, go to Channels > Email Campaigns, click Create Email, then select Block-Based Email.
On the Your Templates page you can choose from any of the available templates. Just hover your cursor over the template and click Create Campaign.
If you want to use one of the prebuilt templates, you will first have to make a copy so that it appears in the Templates section and is available for selection.
Resaving link domain changes
Block-based Email campaigns need to be resaved in Content Creation if the link domain is modified in Email Settings.
In other words, please be aware that if you change the link domain in the (1) Email Settings stage (above), you need to resave your content in the (2) Content Creation stage (below).
Without saving again in Content Creation, all the links in your campaign keep the previous link domain, they do not get updated.