You will only need to this part once.
Open Gmail.
At the top right, click Settings and then See all settings.
At the top, click Advanced.
In the Templates section, select Enable.
At the bottom, click Save Changes.
Open Gmail and click Compose.
Enter the text you want to save.
Click More (three dots at the bottom right) and then Templates.
Click Save draft as template and then Save as new template.
Give your template a name.
Open Gmail and click Compose.
Click More (three dots at the bottom right) and then Templates.
Under Insert template, choose a saved template to insert in your email.
Compose the rest of your message and click Send.