@investacube , I will answer your questions :
1. just add the file and name it single-company.php
2. adjust to your prefrences means , that you will create the html design of the company profile , there is no default template
3. here is an example of simple template
<?php
get_header(); ?>
<?php the_post(); ?>
<header class="page-header">
<h1 class="page-title"><?php printf( 'Jobs at %s', esc_attr( urldecode( get_query_var( 'company' ) ) ) ); ?></h1>
<div class="company-profile-info">
<ul>
<?php if(get_the_company_logo()): ?>
<li><?php the_company_logo(); ?></li>
<?php endif; ?>
<?php if ( get_the_company_website() ) : ?>
<li>
<a href="<?php echo get_the_company_website(); ?>" target="_blank">
<?php _e( 'Visit Website'); ?>
</a>
</li>
<?php endif; ?>
<?php if ( get_the_company_twitter() ) : ?>
<li><a href="https://twitter.com/<?php echo get_the_company_twitter(); ?>">
<i class="icon-twitter"></i>
<?php _e( 'Twitter'); ?>
</a></li>
<?php endif; ?>
</ul>
</div>
<h2 class="page-subtitle"><strong><?php printf( _n( '%d Job Available', '%d Jobs Available', $wp_query->found_posts ), $wp_query->found_posts ); ?></strong> <?php if ( get_the_company_tagline( get_the_ID() ) ) : ?>• <?php the_company_tagline( '', '', true, get_the_ID() ); ?><?php endif; ?></h2>
</header>
<?php rewind_posts(); ?>
<div id="primary" class="content-area">
<div id="content" class="site-content full" role="main">
<div class="company-profile">
<div class="company-proflie-jobs">
<?php if ( have_posts() ) : ?>
<div class="job_listings">
<ul class="job_listings">
<?php while ( have_posts() ) : the_post(); ?>
<?php get_job_manager_template_part( 'content', 'job_listing' ); ?>
<?php endwhile; ?>
</ul>
</div>
<?php else : ?>
<?php get_template_part( 'content', 'none' ); ?>
<?php endif; ?>
</div>
</div>
</div><!-- #content -->
</div><!-- #primary -->
<?php get_footer(); ?>
Most of the functions used in this template will be found in plugins/wp-job-manager/wp-job-manager-template.php