Testing server

I think that this is not too difficult I just can’t see it so if anyone can help I’d be really grateful. I use FTP to up load to my server, the site is in a file called HTML there is another file above this called DATA where I have a database and a fav icon etc it all seems to work just fine except when I try to do anything in dreamweaver 8 that needs a testing server I get all sorts of conflict messages, most of them suggest that the URL is wrong. So the question is - If the site is at

http://www.mysite.com
the ftp is ftp.mysite.com

what is the correct url prefix for the testing server?