I am new to Joomla, just added a website with a new account there today.
By default I am the Administrator (not super) and missing some of the functionalities.
Any ideas ?
I assume you've signed up for an account on Joomla.com. This service has a slightly different setup than a "normal" Joomla installation (downloaded from joomla.org and installed on your own hosting account).
As described in the tutorials:
None of the core Joomla content management function is limited for the Joomla.com users: articles, media, users, menus, components and extensions can be edited as in a standard Joomla CMS. However, no Superusers are allowed оn Joomla.com websites. Тhe installation of the extensions and templates is restricted and the users cannot edit server configuration information.
Further differences between Joomla.com and Joomla.org can be found on http://www.tutorials.joomla.com/basics/16-joomla-com-vs-joomla-org
Good luck with Joomla, I'm sure you'll like it. And don't hesitate to ask if you have another question.
It looks like you are using the free version of Joomla where some functionality is restricted. For example you only have Administrator access.
For full functionality you can upgrade to a paid SiteGround account with your own domain name.
You can also export a joomla.com website via the joomla.com dashboard. The export file includes the website files and database which are sufficient to recreate the website on an alternative hosting server.