Once you've registered a domain with dot.tk, you can use the domain using one of two ways.
1: The first way is the easiest and quickest way to use the domain. Log into your cPanel account at
http://starka.x10hosting.com:2082, and then under the Domain section of cPanel, choose Parked domains. Enter in the name of your domain into the section called "Add a new domain" and then press Add Domain. Once completed successfully, give the server a few hours to update the records for your account and see if the domain is working for you.
2: The second way is pretty much just as easy, though it involves a little bit of waiting. If you visit your account panel at
http://www.x10hosting.com/control , under the "Hosting" option at the top of the page, there is an option to change your main domain name. When you visit this page, click on the check box next to "Use an x10Hosting subdomain as my account's main domain" and then in the box below, fill in your .tk domain name. Click "Update Main Domain" and then give the server a few hours to process the request.
If you need help, or if this wasn't what you were asking for let us know