it's pretty simple and very obvious.. right on the submit page you will see IN RED
"NEW: This text link back to Freeones is required on your gallery: Free Porn"
So You would put <a href="http://www.freeones.com">Free Porn</a> on your galleries.
Also, you will see in the submit form in the section where it says Return link to Freeones: No return link means no listing!
pretty obvious there.