If you design a page and want to use it as a template for other pages, simply drag that page to the "Templates" folder to the left-hand column on your project. Once there, you can rename it and alter it as needed.
Any page can be a template by dragging it into the Templates folder.
Create a duplicate of the page you want to turn into a template before dragging it to the Templates folder. This ensures you don't lose any information you need to continue writing on the page.
Once in the Templates folder, you can edit any page. However, it will ***NOT*** update any pages already created with that template.