Email templates can be saved and loaded from the Email panel within the Utility Panel. After you have written your email, to save it as a template simply click on the Templates dropdown near the top, select Save, and give your template a memorable name. You can then load that template again later by clicking on the same Templates dropdown, selecting Load, and choosing your template by its title.
When a template is loaded, you can even make changes to it and then save that as a new template by selecting Save As from the Templates dropdown.
For more information about sending emails in CATS please see this article.