Most hosters have a standard URL for sites they host.  But  you really need to buy a domain for your site to use permanently and get the domain setup to hit the IP your hoster tells you to use.  Your hoster can tell you what your default URL is so you can use that until you get a permanent URL with the domain you want to use.  Your hoster would also be the one to help you get your domain registered so it is pointing to your site.  If your hoster cannot help you, then I would consider changing your hoster.  Some recommendations for good DNN hosters are IHostASP.net, PowerDNN and WebHost4Life.  If you decide to use WEbHost4Life use the following link so I can get the referral credit (http://www.WebHost4Life.com/default.asp?refid=smehaffie).

Did you register a domain name?  If so, and you did the default install, DNN is at http://www.{YourDomainName}.{Whatever}/DotNetNuke.  If not, check with your host to see what your web site address is and add the /DotNetNuke folder (or whatever folder you installed to).

Jeff