Once you buy your hosting package, they will give you their nameservers, which you then put into the nameserver settings with the company you purchased the domain name from. As Andy said, it then functions a bit like a mail redirect. Be aware the update isn't always instant either, it can take up to 3 days for it to 'propagate' [as they call it] across the internet, so in that time, not everyone typing your web address will necessarily get to your website, although I have always found it is much quicker than that. If you are unsure of any of this, might be an idea to ask the domain registrants for help once you have your hosting package.