Look for the folder name Plugins → Visual Composer in unzipped package downloaded from themeforest.net. This folder contains visual composer plugin zip named as js_composer.zip. This folder also contains visual composer documentation and readme file. You need to go to Dashboard → Plugins → Add New in your WordPress admin side and upload the js_composer.zip as displayed in image below.
Once installed, You need to activate the plugin as displayed in screen shot below.
After activation you can create a test page to try out visual composer.
Click on "Backend Editor" Button in visual composer toolbar, and you will have the visual composer page builder layout ready for use as displayed in screen shot below.
Going Full Width
If you like, You can assign a full width template to the test page.
If you want to disable comments for this page, Then expand the screen options in top right corner and select "Discussion" checkbox. It will display discussion meta box below page editor area.
Un-check the both checkboxes in Discussion meta box and publish/update the page.