Hi,
The "preload" section where you have the PHP code of the email loads all the data used to display the tags in the HTML section of the email.
The template is what contains the CSS, the images and the frame around the email content.
So normally, if you want to change the content, you'll want to edit the HTML/preload areas.
And if you want the change the style / frame of the email, you'll want to change the template. Also, the template is generic so it can be used for several emails.
It's like on a Joomle website: the pages are basically a combination of :
- the content, which comes from the current component and modules
- the layout / style of the page, which comes from the Joomla template