Flash has its pros & cons for websites. It's awful for SEO purposes, and HTML5 is now becoming the norm (much faster, accesible).
That said, you can either incorporate flash elements into a website by using the tag, this can include movies, navigation, into pages etc. You can find more information on that at http://w3schools.com/ in HTML tutorials.
The other option is to make a whole website out of flash which is generally slow, done by a professional and is based on the language of ActionScript - the latest version being AS3.