Can I send the person who completes a Workflow an email?

If you want to send the user who completes a Workflow an email you can do this by creating an email answer rule and specifying the "to" email address as the email address supplied in the Workflow.

Note that you can edit the sender name, subject line and email contents in this same create email answer dialogue.

To edit the sending email address see this FAQ and to change the branding/design of the email that is sent see this FAQ.