With the Flash Player plugin for your browser you can watch movies, animations and games on certain websites. Flash Player is still used a lot - although many websites are looking forward to the switch to the less heavy and safer HTML5. Producer Adobe has announced that Flash will be phased out in the coming years and in most browsers Flash content will only be displayed if you click to activate.
Under Windows you must install Flash Player separately for Internet Explorer and Firefox, Opera and other non-IE browsers. So go to the download page with multiple browsers. This also applies to macOS. Google Chrome has the Flash plugin built in as standard, so you don't have to download it separately for Google's browser. Windows 8 and 10 provide Flash as standard for IE and Edge and update the plugin via Windows Update.
New Android smartphones and tablets (version 4.0 and higher) no longer receive Flash. Flash is also not available on iOS (read here why Steve Jobs did not want Flash on iPhones and iPads, but fully used HTML5).
You can free download Flash Player 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.