If you want to install Flash Player for Internet Explorer on Windows 8 you'll need to upgrade to Windows 8.1. As of Windows 8 Microsoft embeds Flash Player in IE and all updates are distributed by Microsoft via Windows Update. Microsoft recently terminated mainstream support on Windows 8. In order to receive updates (security, etc) you'll need to update to Windows 8.1.
The following resources may be helpful:
If you want to download Flash Player for a different browser (except Chrome) launch that browser and navigate to https://get.adobe.com/flashplayer to download the installer. Google also embeds Flash Player in Chrome, so there is nothing further to install for Chrome.