Plugins are tools which increase your website functionality. To install a plugin you generally just need to put the plugin file into your ‘wp-content/plugins’ directory
Once a plugin is installed, you may activate it or deactivate it from the Plugins menu in your WordPress administration panel.
In WordPress 2.7 and above version you can install plugins directly from the admin area.
Download the plugin to your computer, then log in to your WP admin area and go to Plugins > Add New. search the plugin archive and select it. Then click Install Now and the plugin will be installed successfully.
Click add new plugin in that you can enter the plugin name and click, it will display the list of plugins. Then you can select the plugin and click install.
To remove the plugin just click delete button in the plugin menu.