Can I use FTP before my domain’s dns propagates?
Yes. Use your IP address found in your welcome email as your “host name” and then your user/password. After your DNS propagates you will want to change the host name to ftp.yoursitesdomainhere.com
What is my username/pass/host name to use FTP?
Your username/pass is the same as in your welcome […]

You go to http://www.yourdomain.com/cpanel or http://yourIPaddress/cpanel
Your Control Panel (AKA Cpanel) is the main area where you can access all the necessary tools to edit your website, check stats, and install scripts and do a number of other things.

Yes. Use your IP address found in your welcome email as your "host name" and then your user/password. After your DNS propagates you will want to change the host name to ftp.yoursitesdomainhere.com