To access the Template Editor, hover over the Messages tab in AWeber's control panel, then click the Email Template Manager link.
You will then be presented with three choices:
Start with an AWeber template
This option is for those who want to use an AWeber template without modifying any of the source code. You can add content to a message and use it as a "starting point" when building new emails.
Import a Template
This option is for those who have a coded email and want to port it over into AWeber but are not as familiar with HTML. Our drag and drop editor allows you to add "dropzones" into your template so it plays nice with our message editor.
Code Using Our Theme Language
This option is for those who are familiar with HTML/CSS and are trying to get the most out of our editor.
Pick the third option "Code Using Our Theme Language".
In this mode, you can give your template a name (what the user will see in their template gallery), add any needed styles via the CSS button, and of course, code the template itself.
Note that you can collapse each section of the template you're working on by clicking the header. Just below the header, you'll find a list of any required or optional variables that can be used when coding that section.
The Documentation and Code Example link under each section provides an overview of the purpose of the section in question, as well as some basic examples and rundowns on the available variables.