Sometimes, a site will be submitted by a guest who later registers and wants to go back and gain access to edit what they submitted as a guest. WSN's claims system can handle this automatically.

When you enable the "allow claiming links" switch at Admin -> Settings -> Switches, an area appears on the member home main page (the page they reach by clicking "Options" in the top menu bar, profile.php) which explains to users that they can place a certain code on their site to verify that they own it, and then type in the URL there to claim it. The claim is processed automatically if they prove their ownership of the site.

If topics don't have URLs associated with them, there's no automatic way to verify ownership. In these cases, you'll have to allow them to contact you through the contact form (assuming you have the contact form switch) and process it manually.