If you dont want to code you can install this ready to use wp edit header and footer plugin.
Hi, when you develop a plugin or theme. You will need to add come codes to header or footer section. With this action hook “wp_head” you can add any php , css , js code to your header in your plugin or theme.
<?php
add_action('wp_head', 'gc_add_header_code');
function gc_add_header_code() {
// your codes
}Be carefull when you add js or css code because you need to close php tags first.
You can use this example when you add css or js codes.
<?php
add_action('wp_head', 'gc_add_header_code');
function gc_add_header_code() {
?>
<style>
</style>
<script>
</script>
<?php
}