First you need to log into STORM
Once logged into STORM, you will be taken to the STORM dashboard.
From the STORM dashboard, click on Websites.
Click the cog icon next to your website to manage your website.
Click on Staging
Do note that the Staging section won't show up unless you specified a CMS when Setting up a Website either as a fresh install or just moving an existing one.
Here you can make some changes such as Enabling Password protection or Disabling Search engine from Crawling your site, as well as changing the name of the staging site. The Default for the staging site name is staging.DOMAINNAME.com
Click Create Staging Website once you've made your changes
Storm will now go and make your staging website, depending on the size of the website you're copying it can take anywhere from seconds to minutes.
Whilst this is going on it's worth checking you've got valid DNS setup for the staging site.