Welcome to the forums seaofbass
Start by transferring your content over to the TCH Servers. You can use the IP address provided in your welcome email.
After you have your content on the TCH servers you can then transfer your domain to TCH and that is where you will use the authcode. You can call a Transfer Concierge anytime! 1-480-505-8866. They can only help with the domain transfer and not the content.
http://www.securepaynet.net/default.aspx?prog%5Fid=simple
Or if you aren't transferring the domain, you would then change your name servers at your registrar using the ones listed in your welcome email.