To install a plugin you just need to put the plugin files into the wp-content/plugins directory. Once a plugin is installed, you may activate it or deactivate it from the Plugins menu in your WP administration.
Download the plugin to your computer, then log in to your WP admin area and go to Plugins > Add New.
Browse to the plugin archive and select it. Then click Install Now and the plugin will be installed shortly.
after successful installation then click on activate.