You might see a notice in the Dashboard about the need for providing a purchase key and activating WPBakery Page Builder and Revolution Slider.
WPBakery Page Builder and Revolution Slider are included in the theme on extended license, which means we bought them for a higher price to be able to include them in our theme. You as end-user can use these plugins only with this theme without the need for a license key.
Updates of these plugins come with the updates of the theme. We always include new updated plugins in theme a few days after release.
If you want to access auto-updates and to get help from the plugin author you can buy your own license but that’s not necessary.