You can write texts for letter templates that you can then use again at a later time. Once a template is created, you'll be able to select it from the drop down menu at the top right corner of the letter window.
You can create and manage your letter templates in the letter window:
Create letter templates
When creating a letter in the letter window, you have the option to save that letter as a template. Simply select Save this letter as a template... from the drop down menu in the upper right corner.
Once selected, you'll be asked to pick a name for your template. Once the template saved, it will appear in the list under Template.
Select a letter template
While creating a letter in the letter window, you can select a template you want to use. Simply select a template from the drop down menu Template in the upper right corner. This will load the content of the template into your current letter window.
Manage letter templates
You can rename or delete the templates as well. Simply select Manage templates... from the drop down menu in the upper right corner. This will open the Manage Templates window:
To rename a template, double-click on its name or select it and press the "Edit" button.
To delete a template, select it and press the "Delete" button.