Extract the package downloaded from ThemeForest to your desktop. In the extracted package you will find"hague.zip" which is the WordPress theme file.
You can install the theme one of two ways:
Extract the hague.zip file and upload the extracted folder to the /wp-content/themes/ folder on your server.
Navigate to Appearance > Add New Themes > Upload page. Select the hague.zip file. Press the Install Nowbutton to upload and install the theme.