Insert code snippet in the header, footer and functions.php of your Wordpress.
Download it compressed in zip, in the plugin panel of your WordPress select upload plugin, then activate it.
You will be able to create them independently and thus have them fully controlled, being able to enable or disable any of them at any time.
Note: When you create a new code fragment for the header or footer, we consider that you want to include javascript or css, in either of these 2 cases use the corresponding opening and closing tags
# using css
<style>write your code here. ..</style>
# using JavaScript
<script>write your code here...</script>
In the case of creating code fragments for functions.php, no tag for php is necessary, I leave you an example for a new code fragment for functions.php
# Modify the footer text in the administration part
function custom_text_footer_admin() {
return 'Thank you for believing in ...';
}
add_action( 'admin_footer_text', 'custom_text_footer_admin' );