You can use an existing email newsletter as a template for future newsletters.
Start by creating your first newsletter. Full instructions are in the article, Creating Newsletters.
Once you've saved the newsletter in a format and layout you like, click the Newsletters link in the Publish tab and find it in your list of newsletters. Click the green swish icon
to the right of your newsletter to open a new editable newsletter using this one as a template.
You may simply replace old text and images (including the title, which otherwise defaults to the original newsletter title with the suffix "- Copy") with new text and elements (images, inserted marketplace items etc) as you go, and repeat this process each time you want to start a new newsletter.
Or, you can change the title of this newsletter to "Template" or "Template A" etc. as you see fit, change all the text and images to placeholders (such as the word "Title" and a paragraph of "lorem ipsum" placeholder text or even just the word "text" or "copy") and save the newsletter as a dummy to be reused in future.
To reuse your template, find it in your list of newsletters, click the green swish icon
to the right, and edit the title, elements and text as desired.
Always remember to scroll to the bottom and click Save when you've created a new newsletter.
Related Article: Creating Newsletters