Emails can be made within MailChimp or created outside of MailChimp and imported.
Editing within MailChimp
As you're setting up a campaign, you'll get to the Template section. Choose the "Saved Templates" option. Choose the template that's appropriate for your content.
Hover over the content to see the editable sections.
Up-Down Arrows: Click and drag to rearrange the section
Plus Arrow: Click to repeat the section
Minus Arrow: Click to delete the section
Edit: Click to edit the section
The initial edit view is ideal for making simple text changes.
For further changes, it's often easiest to edit from the code view (click the
Editing outside of MailChimp
Emails written in MailChimp's template language make them editable in the MailChimp Editor