The Polygon Documentation
As mentioned already in the previous pages of the documentation, the theme packet you download from your YIThemes account includes three different ZIP folders in it:
the first one contains the theme and the second one ("plugins.zip") includes the three premium plugins that you have to upload manually into your WordPress
The three premium plugins included are: WPBakery visual Composer, Slider Revolution and Ultimate Addons for Visual Composer.
WPBakery Visual Composer
If you need to read more about this plugin, you can read the official documentation of WPBakery Visual Composer.
Read the official documentation of Slider Revolution if you had any doubts about how to use it.