My header not showing up [closed]

Simply having a header.php in your theme’s folder will not output your header to the browser. You have to call the header too.

To call the header.php file, you should use get_header(); at the top of almost every template (Almost!) such as page.php, single.php, archive.php and so on.

Do the same for footer.php to get the footer.

I can’t quite recall the full list, but these are the main files:

archive.php
author.php
category.php
date.php
front-page.php
home.php
index.php
page.php
single.php
singular.php
search.php
tag.php
taxonomy.php

This also applies to child pages, and child theme’s pages, such as page-abc.php.

Also, take a look at the WP Hierarchy schematic. This is greatly useful for those who want to start developing themes.