get header in wordpress

Hi,

I have a page that I created inside my wp-content/themes/mytheme
Inside I put this:
<?php get_header(); ?>
My Code
<?php get_footer(); ?>
But I get the error that it doesn’t find the function get_header();

Searching in internet I found that I have to put:

require('./wp-blog-header.php');

But if I put this require It loads more than I want. I mean more code, I just want the styles, the sidebar, etc

Any ideas?

Thanks!