Automatic installation of a plugin is easy and you can also install one manually. It will involve manually downloading a plugin, uploading and activating it.Make sure you already downloaded a zip file of the plugin to your computer.
1- Login to your WordPress admin dashboard.
2- Under the dashboard menu, hover your mouse over Plugins and click on Add New.
3- Click on Upload Plugin and then on Browse. Chose your plugin's zip file and then click on Install Now.
4- Click on Activate Plugin.
Note: The newly activated plugin will show in the sidebar menu. If a setup of the plugin is required, it will show an option to complete it.