Plugins are utilities which provide additional functionality to your application.
To install a plugin you just need to put the plugin files into the wp-content/plugins directory. Once a plugin is installed, you have to activate it to start its functions.
Earlier we had to get in to the file manager part to put the plugin files into the wp-content/plugins directory But In WordPress 2.7 and above 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.
Browse to the plugin archive and select it. Then click Install Now and the plugin will be installed shortly.
After the installation,you need to active the plugins for the plugins to start functioning.
Note: you can deactive plugins anytime ,if you dont need it in future.
Read our article How to delete the plugins from the wordpress blog