Check out example codes for "what is bootstrap". It will help you in understanding the concepts better.

Code Example 1

Bootstrap is a free and open-source CSS framework directed at responsive,
mobile-first front-end web development developed by TWITTER

It contains CSS- and JavaScript-based design templates for typography, forms,
buttons, navigation, and other interface components.

Code Example 2

Bootstrap is a CSS Framework developed at Twitter.
It aids in the rapid prototyping of Web Application styling.

Code Example 3

<div class="jumbotron text-center">
  <h1>My First Bootstrap 
  Page</h1>
  <p>Resize this page to see the responsive 
  effect!</p> 
</div>

<div class="container-fluid">
  <div class="row">
    
  <div class="col-sm-4">
      <h2>London</h2>
      <p>London is the capital city of England.</p>
      <p>It is the most populous city in the United Kingdom,
      with a 
 metropolitan area of over 13 million inhabitants.</p>
    
  </div>
    <div class="col-sm-4">
      <h2>Paris</h2>
      <p>Paris is 
 the capital of France.</p> 
      <p>The Paris area is one of the largest 
 population centers in Europe,
      with more than 12 million 
 inhabitants.</p>
    </div>
    <div 
  class="col-sm-4">
      
 <h2>Tokyo</h2>
      <p>Tokyo is the capital of Japan.</p>
      <p>It 
 is the center of the Greater Tokyo Area,
      and the most populous 
 metropolitan area in the world.</p>
    </div>
  
  </div>
</div>

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