1. To install a plugin click on the Add New link under the Plugins section of the sidebar in the WordPress admin panel.
2. Next search for your plugin. Either put in the actual name of the plugin you are looking for or keywords for the feature you want.
3. Find the plugin you want through the search results and click Install Now.
4. Once your plugin is installed, options for your plugin are generally added under the Settings section of the sidebar in the WordPress admin panel. Depending on your plugin, the options page may be added elsewhere (i.e. under Tools or within its own section).
See more tutorials in the WordPress Handbook.