Extract the zipped package downloaded from ThemeForest to your desktop. In the extracted package you will find the johannes.zip file which is the 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 johannes.zip file.
Watch the complete installation process in this short video:
Extract the johannes.zip file and upload the extracted johannes folder to the /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 the Appearance -> Themes page to activate the theme.