Nebula has many built-in custom shortcodes. You can see full lists of them from demo site. You can also use shortcode generator to generate sample code of theme shortcodes.
Go to Pages and edit or add new page. You will find Shortcode Options box at the bottom. Select Shortcode you want to use and fill all options then click Generate Shortcode
Limitations
Tab Shortcode is not support in Shortcode Generator. You can find tutorial about how to use it here.