There are two ways to create an email link (one that will send an email to a specified address):

Simple method

Type the email address in the text editor window. Drupal will automatically recognize it as an email address and convert it to a link when the page is viewed.

Advanced method

If you don't want the email address itself to be visible in the text, you can create a standard link instead, using any text.

Highlight the text and click the Linkit icon as when creating any other link.

In the path, field, simply type mailto: followed by the email address (do not include any spaces).

This will open a new email in the visitor's email application with the chosen email address as the recipient.