Begin by clicking “Add new” below the editor window. Now name your new template and choose if you want it to be based on the “default” template or you will choose its design later from the predefined templates. Now click “Add template”.
If you chose “Empty template”, you can now browse the predefined templates by clicking on “Choose design” button on the top right side of the screen.
Here you can switch between various predefined templates - choose the one that is the closest to ideal and you will save time editing it later by clicking on “Load design”.
If you chose “default” in the “Based on template” window, you essentially made a copy of the default template. You can use this later to make copies of any templates.
In both cases, you now have something that looks similar to this: