A shortcode is a WordPress-specific code that lets you do nifty things with very little effort. Shortcodes can embed files or create objects that would normally require lots of complicated, ugly code in just one line. Shortcode = shortcut.
Get started by clicking the + Inserter icon 
at the bottom-left corner of the screen and select the Shortcode Block from the blocks list
It will look like this once you add the block:
You may type your shortcode into the box provided or paste it from the available shortcodes.
