You can install the plugin in two ways. 1st way is via WordPress Dashboard and 2nd way is via FTP.
Installing via WordPress Dashboard
Visit Plugins > Add New page and search for Directorist in the search box. Install and activate the Directorist – Business Directory Plugin from the search result. After activating the plugin you will see a new menu called Directorist Listings added to the WordPress Dashboard menu.
Installing via FTP
At first download the plugin file from the WordPress plugin repository. Login to your hosting using an FTP client and upload and unzip the file inside the plugins directory usually found in your hosting server’s /username/public_html/wp-content/plugins/ directory.