Actually I want to create webpages dynamically. How can I do it?

 Your question is a little broad. You can create templates that have dynamic content such as a shopping cart. What kind of pages or content are you trying to generate dynamically.

Do, you want to create aspx pages dynamically,

I dont find any reason for that, as you can dynamically change the content on page while loading

 

Do you mean  Create HTML Dynamically, then use xml as datasource and xsl as presentation layer,and css for styling, and you have your HTML ready.
 

The way some pages with url rewriting work might confuse one to think that all the page names in the address bar are for real pages that exist.

Example can be where you have many different news with different names in a news site . But here what happens is rather than having a page for each news, having a template page which

 dynamically gets filled with data for the news. After this, even if your page for a certain news is news.aspx?id=23 , you have it shown as  titleofthenews.aspx in the address bar of the browser(although in reality it is news.aspx?id=23 )

 http://www.urlrewriting.net/en/Default.aspx