Flash Player is free software that lets you view web content created by Flash. This content may be interactive content such as menus that slide, or may be complex applications, games, or animations. Many web browsers (Internet Explorer, for example) install Flash Player automatically, but you may need to upgrade it from time to time as Adobe makes improvements and as websites you visit update their content.
Websites that contain Flash content require the Flash Player. A message asking you to download Flash Player comes from either the website you are viewing or from your browser. Most browsers come installed with Flash Player, so you may already have a previous version of Flash Player installed. You may still need to update to the latest version if the website contains features that require a newer version.