How to write page.tpl.php where the HTML files is more than one? I'm using Drupal 7 and trying to set my custom theme up.

I usually replace the index.html to page.tpl.php, then I change what I want it to be dynamic on my site. But now I have more than one HTML file which is about.html, blog.html and contact.html

Can anybody explain to me how to write that?
Actually you may have to create a page--front.tpl.php for index page of your website and a page.tpl.php to have all other pages.

you could also use theme debug mode too. it can be enabled by including the following in settings.php,

$conf['theme_debug'] = TRUE;

The ablove will include theme suggestions as html comments, that helps you theming your pages.