you need to update the DNS name servers to point to your host.
Is it hosted by the same place you got bought the domain name from?
eg. you have your domain registered with domain central and hosting with bigpond.
you need to login to your domain central account and change your DNS nameservers to whatever bigpond specifys. Maybe - ns1.bigpond.com and ns2.bigpond.com
- this is just an example, login to your bigpond account to find out the right names etc.