First, open the needed step template in your sequence. Then select the HTML editor option from the toolbar (if you don't have it, make a request to enable it for your account):
Insert the code <a href="{{SomeUrlVariable}}">Link text</a>, where:
{{SomeUrlVariable}} - is your custom variable with a link
Link text - is hyperlinked text
Another option is to hyperlink text from the template directly
1) Select text to hyperlink
2) Click on hyperlink icon
3) Enter the name of the custom field with a link. Please make sure to copy the name correctly from Variable section
