A layout is a pre-defined email structure to use when creating the email draft. There are 5 layouts to choose from.
On the toolbar within the email edit screen is an icon labeled Layouts (see image). Clicking on the icon will open a window for you to select one of the available layouts.
Select a layout from the list and it will load into the email draft for editing.
Simply delete out the placeholder text and add your own content. The layout will keep the structure of your email intact.
If you use a layout with an image, right-click on the image space-holder then click Image Properties to insert your image.