you can always make a google search. in short dynamic sites uses server side scripts to process the dynamic requests. php, asp .net are some of the languages used for it.
if you are really looking for how to build and manipulate dynamic websites, webcosmo is right. You need to study up on php or asp .net. I would recommend PHP for a first time programmer. if you are looking for a way to make a dynamic website, with having to learn minimal programming and using other developers code and plugins, you should look into a Content Management System(CMS). Common CMS systems include: Wordpress, Joomla!, Drupal, and MODx
We have a VERY easy to use CMS system for people who don't have time or inclination to learn complex things! Try easyCMSlite. There is a link to a fully functional demo there too, so you can try it before using it. Its is free!