WordPress plugins are software that can be used to extend and expand the functionality of your WordPress site, for more details, refer to https://wordpress.org/plugins/.
Using WordPress Toolkit you can install plugins on one or more WordPress installations from within your Plesk control panel.

Installing Plugins

1. To install a plugin on one or more WordPress installations, Login to your control panel
2. Go to Websites & Domains 
3. Click on WordPress
4. Select Plugins tab
5. Click Install
6. In the search box type the name of plugin which you want to install
7. Select the desired Plugin from the list desired plugin in the list
8. If you want to activate the plugin quickly after the installation Check the checkbox Activate after installation 
9. Select Instance and Click install button

Removing Plugins

1. Login to your control panel
2. Go to Websites & Domains
3. Click  WordPress
4. Select Plugins tab
5. Check the checkboxes next to the plugins names you want to remove 
6. Click Uninstall

Activating/Deactivating Plugins

1. Login to your control panel
2. Go to Websites & Domains 
3. Click  WordPress 
4. Select Plugins tab
5. Check the checkboxes next to the plugins names you want to Activate or Deactivate 
6. Click Activate/Deactivate