Switch to HTML view:
Scroll down to a "section" (line 570 in the screenshot), you will want to duplicate that part, alternative remove it if fewer sections are wanted.
This is a full section highlighted. Copy this into your clipboard by right clicking on the highlighted area and selecting "Copy".
Right after "end of section" you want to paste your clipboard (right click at the location then select "Paste").
Two small things needs to be modified in this newly pasted section:
The "name" of the editables needs to be unique within the template (see highlighted area in screenshot above). In the above we changed "article1-h3" to "article2-h3", and "article1-text" to "article2-text".
Note: if the names are not unique in the template, you will struggle changing the content as SendCastle will not know which editable you are actually modifying.