8453 is a cover page that you print and mail to the IRS along with some other document that the IRS needs by mail, after you e-file. The most common form that needs to be mailed to the IRS is form 8332 dependent release in custody cases, but there are a few other things that may be needed.
Print a copy of your return and read the instructions carefully. If you need to mail a form to the IRS and don't, your refund could be delayed or you could be audited.