How to display user-defined / custom post in wordpress?

Try below code

index.php

<?php 
$args = array(
       'post' => 'people',
       'post_status' => 'publish'
       )

 query_posts( $args ); ?>

<?php if ( have_posts() ) : ?>


 <!-- the loop -->
 <?php while ( have_posts() ) : the_post(); ?>

   <?php get_template_part( 'content-templates/content', 'people' ); ?>

 <?php endwhile; ?>

<?php else : ?>
 <?php get_template_part( 'content-templates/content', 'none' ); ?>
<?php endif; ?>

content-people.php

<div class="col-lg-3 col-md-6 text-center">
<div class="service-box">
   <i class="fa fa-4x fa-diamond text-primary sr-icons"></i>
       <h3><?php the_title(); ?></h3>

</div>

Hope this will helps you.