Open Gmail and sign in
Click the Settings gear icon
Select See all settings
Go to the Advanced tab
Enable Templates
Click Save Changes
Compose a new email
Write the message you want to save as a template
Click the three-dot menu in the compose window
Select Templates
Click Save draft as template
Choose Save as new template
Enter a template name
Click Save
To use the template, open Compose
Click the three-dot menu
Select Templates
Choose the saved template
Edit if needed and send the email