Plugins allow users to expand the functionality of their blog in various ways. Plugins are pieces of code that perform some function, say for example a plugin might allow you to display weather forecasts in your sidebar. In WordPress, you need to activate a plugin before you can use it.
Clicking on the Plugin tab will bring up the Plugin Management page. Here you’ll see a list of all the plugins that are available to you and whether or not they are active. Toggling the Action button will activate/deactivate the plugin.
Depending on how the plugin is designed will affect how you interact with it. A plugin might add a sub-menu configuration tab, or add functionality to the Visual Editor. A plugin will most likely not add a new menu tab, as that behavior is not recommend in the guidelines for plugin development. Clicking on a plugin name will take you to the plugin’s home page which may or may not be useful for learning how to use the plugin.