You'll want to use a program like cuteFTP or FileZilla to transfer your files via FTP. CuteFTP you can use the trial version for free (for however long you want) and File Zilla is totaly free. But I think CuteFTP is a little easier to use for somone new to FTP.
You'll just set up the program to connect to your website - when it asks for the doamin to connect to just enter yourdomain.com as well as the user/pass you set up for the domain. (not necessarly what you use to log into the panel with, but the user you set up in the panel.)
Once you've connected sucessfully, you get a directory listing, you should see logs, maildir, and yourdomain.com - Just place the website files in the yourDomain.com directory and then you should be able to see your website when you go to www.yoourdomain.com in a browser!
Please feel free to post back with specific questions.