Flash is used to create content for Web Applications, Vector Animation, Games, Videos, and Mobile Phones. Flash is supported by all browsers and operating systems thus making it an extremely valuable form of visual/audio communication.
Hypertext Markup Language is the predominant markup language for the creation of web pages. It provides a means to describe the structure of text-based information and by supplementing it with interactive forms, embedded images, and other objects makes it the fastest and simplest way of getting your site done.
A server-side language (PHP, ASP, CFM...) using a database enables easy creation/maintenance of large scale sites with secure login system enabling you to insert content into appropriate forms and pre-programmed scripts will create pages dynamically for front end users to view. Dynamic sites can be built for HTML and flash sites.