Adding a new plugin in WordPress can be done in a number of ways. The easiest of which is directly through your WordPress admin area and the process will depend on whether you are wanting to upload a plugin file or search and install directly from the WordPress plugin repository?
When logged in to your WordPress admin area, navigate to Plugins and Add New. From here, you can either enter the name of the plugin you are looking to install or click Upload from the top of the page to upload a new plugin file.
You can also add a new plugin via FTP or File Manager on cPanel into the following folder: wp-content>plugins
