To import your own template into Sentori you must upload the HTML and images (unless they're hosted elsewhere) in a Zip file with the following files and structure:
Note: by default Macs will automatically create a sub-folder inside a Zip file.
Once your template is uploaded, you can then click its cog button and select Edit Default Content & Layout. This allows you to go into the editor's content mode and layout mode in order to make changes to the template. Any changes you make here will be picked up the next time someone creates a new email using your template.
You can copy your template and create variations of it using the above technique. This can be very useful to provide a series of default starting points for different types of email.