DNN builds its pages dynamically every time you view a page.  The page is based on a number of things including the site Skin, container Skin, the modules loaded onto the page you selected and the contents of these modules.

A such saying how can i put some html I copied from some other site needs to be backed up with a lot more information.

In theory you could put html from another site into a HTML module - but is a pretty safe bet that this may not work out as you would expect.

A better question would be for you to explain what you are trying to achieve in more detail and see if there is some help available.

Westa