I am in confusion , i know some use wordpress , some drupal , but i want to know , what CMS they use to edit HTML pages , like they have login for admin page , sitename.com/admin in that admin , there is only basic options of editing pages only. what is it? see the login picture looks like this (attachment) , and i need to know what kind of CMS is that . please let me know thanks.
I guess if it's really basic it's a selfmade CMS or for example a wordpress blog which was completly reduced in functions for the backend. I myself prefer to work with wordpress as you can realize nearly everything based on wordpress.
In order to know what CMS that is specifically you need to view the source code of the page and look for tell-tale signs of what CMS it is. There will be keywords for wordpress, drupal, etc. As well the structure of the HTML, the stylesheets used etc. you can tell what CMS it is (if it isn't something custom developed)
First you can aware of the structure of the CMS framework. All framework are totally based on MVC structure. So you can't add the direct Html and PHP code in to that. You can find the particular files and customize that files according to your needs. or you can use the available modules for that.