In order to use your web hosting account at SiteGround with more than one domain name, you need to make sure it allows addon domains.
This feature is available in higher hosting plans like Hosting PLUS, Semi Dedicated hosting, etc. If you are using the Standard shared hosting by SiteGround, but want to use the addon functionality you need to upgrade your hosting plan from the Order section of your Customer area.
Please note that if you wish to have a new domain name pointed to your account, you need to register this domain and this can be done from your Customer Area > Order Domains.
Once you have the right plan allowing addon domain functionality and the domain name is registerred you need to set up your addon domain through the cPanel -> Addon Domains section in order to activate it. Click here for more information on how this can be done.
Alternatively, if you don't want to have separate websites but just separate domains which load the same website, you can park your existing domain names to your primary one. This can be done in any web hosting plan. You can park your domains from your cPanel > Parked Domains.
If you are having problems using your account with more than one domain at your current host, you can sign up for our cPanel hosting package. SiteGround's support team will happily assist you with configuring your account to work with more than one domain.