Click on the "Marketing" icon on the left, followed by "Email Marketing".

From here click on "Non-graphical Templates" then click on "Create Template".

Add a Name, Subject Line, Category, and the body of the Email Template. You will also be able to add any file from your Library by clicking on the "Marketing Collateral" Icon. Once you are happy with your template, click on the "Save" Button at the bottom.

To use the template in a campaign, you'll want to click the dropdown and click "Create Campaign". This is also the dropdown you'll use to "Duplicate", "Edit", or "Delete" a template