Extract the zipped package downloaded from ThemeForest to your desktop. In the extracted package you will find the opinion.zip file which is an installable WordPress theme.
You can install the theme in two different ways:
1. WordPress theme uploader
Navigate to the Appearance -> Themes page to access the theme uploader screen and use the opinion.zip file.
Watch the complete process in this short video:
Extract the opinion.zip file and upload the extracted opinion folder to /wp-content/themes/ folder on your server. You will have to use FTP software like FileZilla.
After uploading the theme, you have to activate it. Navigate to Appearance -> Themes page to activate the theme.