How can create a new content

Hi!

I am Pushker Pandey new in Drupal. I want to know if we modify the existing theme with additional(new) content .

Let i have added

<div id="right_content">
		 <div id="first_rightsidebar"></div>
		 <div id="sec_rightsidebar"></div>
		 <div id="third_rightsidebar"></div>
	       </div>

Then how it will show in Block , so that if i want my content on this portion , they display there.

How all above process done?

Please guide me.