When you select the HTML editor from the Email Detail page (the first time), you will have the option to either create from existing templates or to create from scratch.
Note: you need to enter an email name and product before you can use the html editor. Because the predesigned templates and image library in the editor depend on the product.
Creating from predesigned template:
You can select a predesigned template to start editing your email. This will make life easier. Click on the template you want to use, you will be directed to the HTML email editor with the template, ready to start creating.
Creating from scratch:
If you want to design your own layout, you can create an email from a blanc slate. In that case, select the button "From Scratch" in the top. You can now start working on your email by clicking content elements from the menu located on the right and dragging them to the editing area to the left.