A hyperlink is a link to another website or file, activated by clicking on a highlighted word or image in the email body/signature.
How Hyperlinks Work
A hyperlink can be added to any email template by highlighting the text or image you would like to be the hyperlink and clicking the "Add or remove link" button. More information on email templates can be found here: Creating Email Templates
Hyperlinking an Image
You can also select an image and hyperlink it to create a clickable picture or button in an email.