Actually gmail has not pre-installed feature of email templates you have to do it manually that  just requires 2 minutes to set it up

just go to you setting the following snap shows you how to go to settings









First click on “compose ” lable then above window be shown.

next go to your labs section the procedure you can see there in the following picture

and next gmail would prompt to you what you should do now and save that template and you can use it whenever you want.