Adding a New Site
First add a domain to WPMultiSite then add the domain to your hosting account. The only thing that you need to do differently with a WPMultiSite site is to point the domain to your existing installation of WordPress. Usually your control panel will probably want to create a new directory for each domain. In this case you don’t want to do this. CPanel and most other hosting control panels allow you to do this pretty easily. It’s usually one of the last options on the page as this is not typically done.
Here’s what it looks like in CPanel:
Once you’ve got your domain mapped to the directory where you have your WPMultiSite installed you can just browse to the domain name. You should be prompted as usual by WordPress to give your site (blog) a name. At this point you’ve got a new WordPress site setup. You’ll notice that you have all your plugins and themes already available. This is because you’re content directory is shared. (This is typically the case, but it’s possible to have unique content a directory.)