After you click on the link above, enter your existing domain name in the search box and click the transfer button. Once you complete the sign up, you'll receive complete instructions on how to finish the DNS transfer, including how to point your existing domain to your Netfirms website. (Please note: With a DNS transfer, your billing and domain name management remain with your current registrar.)
If you already have a web host, obtain from them the names of their primary and secondary nameservers. Don't worry if you don't understand what these things mean. Just save the information somewhere. The information can usually be obtained from their FAQs or other documentation on their site, usually under a category like "domain name" or "DNS" or "domain name transfer" and the like. If you can't find it, email them. You'll need the information to point your domain name to your website after you buy your domain. Having said that, if you don't have a web host yet, don't worry. Just read on.