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