Step 1: Activate Gmail Templates (aka Canned Responses).
Click the Settings gear in your Gmail’s toolbar -> Select Settings from the menu. Go to the Labs tab and make sure Enable is selected for Canned Responses.

Step 2: Save Canned Responses
Compose the email message that you would like to have as your canned response. Then click the down arrow on the bottom-right-hand corner of the compose window, hover over Canned responses, then click New canned response…
Step 3: Insert Canned Responses Into Email
Start a new email by hitting Compose, click the down arrow on the bottom-right-hand corner of the compose window, hover over Canned responses, then click on the canned response name under the Insert section.