Error using index.php page not working

Hello, I am using wordpress with Xamp and this error has happened.

Fatal error: Call to undefined function get_header() in C:\xampp\htdocs\wordpress\index.php on line 10

I tried to alter the sidebar and saved it in filezilla then this error comes up so I ended up undoing what I did in note pad. It still not working. Any ideas. I’m very new to this. Thanks
<?php

/**
* Index main page
*
* @package SimpleMarket
* @subpackage Template
* @since SimpleMarket 1.0
*/
?>
<?php get_header(); ?>

<section id=”content” role=”main”>
<?php while ( have_posts() ) : the_post();
get_template_part( ‘content’, get_post_format() );
endwhile;
simplemarket_pagination(); ?>
</section>

<?php get_sidebar(); ?>

<?php get_footer() ?>