You can learn how to create and edit email templates by reading this article. If you specifically want to add a gallery's password to your email template, the following steps can get you there:
While you are editing your email template, click the spot within the template that you'd like to add the password to. For example, you might write: "The password for this gallery is: ", and your cursor should be placed after "is: "
Click the Dynamic Content button found on the top-left side of the email template editing area, and choose Gallery: Password.
Clicking the Gallery: Password option will cause a keyword to be placed within your document where the cursor was located. This keyword will automatically be replaced with the correct gallery passwords when each email is sent.
Click Save Email Template to save your changes.
