After uploading your website to your SME server like arno has described, you will then need to redirect your domain to your server:
First, if you don't have a static IP address from your ISP, then you may want to register at dyndns.org (just click on Dynamic DNS after registering at the site to setup a hostname that corresponds to your current public IP address).
If you have a domain name, then go to site where it was registered and login so you can manage your domain. You can either redirect your domain to your IP address or hostname registered at dyndns.org.
However, hopefully you have the option for full dns control so you can create a A host record to your public IP (or hostname from dyndns.org) as well as an mx record for getting email to your sme server.
If you don't have a registered domain name, then just access your website with your public IP address or hostname in the address bar.
This setup is assuming that you have your Cable or DSL modem connected directly to your SME server. Otherwise, you will need to use port forwarding so you can forward port 80 to the private ip address of your SME server.
There are so many different sceneros that can be used when hosting but hopefully the steps above will help; otherwise just post additional information about your setup and if you have control over your registered domain name so I can be more specific in the steps to take.
Nathan