Plugins can be found on the WordPress Plugins Directory or on an external website like a store or the creator’s website. All searches done through WordPress are plugins that are in the WP Plugin Directory.
To search for plugins through the Wordpress Plugin Directory, visit http://wordpress.org/plugins. Using this directory, you can search for plugins by using the search bar or browsing the categories and tags. Each plugin has its own page with information about it. That page has a description, features list, download links, screenshots, creator information, support forum and more. You can also download the plugin from that page and use one of the manual installation processes.