I'm assuming that you've registered a domain name separately from having a hosting account i.e. it is with a registrar who require a name server (known as DNS server) to be specified to point your domain name to some DNS server on the web which starts the chain of how your domain name is used to locate your physical website.
You can have a look at your current DNS server that your registrar allocated by using
http://www.allwhois.net or one of the many "Whois" domain searches on the web.
Your host should have a DNS server that you can request your registrar to point to. If the host will not offer this service, then there must be a URL or IP address to get to your website.
If you have an IP address or URL and your host will not offer this server, then look for a normal service (possibly free but free does not mean reliable!) where you can create a webpage with a redirect on it to your webpage (if URL only) or just use their DNS service if IP address is only available. This means, however, that your site could potentially be slower since all users will be redirected.
This is a lot of hassle and you may be better off just finding a new host that will accept your domain name. Majority do.
Good luck.